Can I use just half the biwire?

Don't leave them hanging. Double them up and use them on the speaker binding posts. You'll benefit from all the conductors being connected.

I don't know if it's kosher, I would say not, but I had a set of biwire cables that I used on my main speakers, and when I would occasionally switch to a small pair of Celestions that were single wire, I would use those cables with the unused set dangling, and I had no ill effects. 

What lowrider57 said, +1. There’s no reason, what-so-ever, to let that cabling go to waste.  Just be certain to get the polarities correct.

I should have mentioned: I cannot double as they're bananas all around. I could get adapters for the dangle pair of course, but, does dangling actually hurt anything? 

If you want to use them that way put some shrink wrap or electrical tape on each dangling end to prevent an accidental short.

I’m just thinking off the top of my head and I use Purist shotgun biwire Museus cables but if you only connect it as a single run cable are you using only half of the wires capability? I’m thinking if you have a 12 gauge wire x 2 and you only connect one of them are you using only half of it’s potential? I'm thinking impedance and resistance differences here. Any feedback on this

@boss302 - That’s why Lowrider and I, responded as we did(ie: 2 x 12 AWG = 9 AWG).

short answer:
cut the bananas off and strip the insulation back and use bare wires if it is a push button opening affair.

I own a pr of speakers with push buttons that open so bananas can be pushed in from top or bottom, but not open enogh for two conductors to fit in well. bummer if that is your situation..

otherwise:
I’ve used bi wire spkr cables since, forever. some of these cable makers construct their bi wires so one half is tuned to the upper end, and the other pair is for the lower end drivers.

I’d spend tthe 10 or 20 bucks on adapters to get both pairs onto the speaker binding posts if it were me.

this is of course with the understanding those banana plugs don’t unscrew any so the other pr of spkr wires can be fit into the slots made available as the plug is unscrewed.

why bother?
1 as said, you’ll have a better conduit for the signal with more strands attached.
2 they might just be ‘tuned pairs’ aimed at or for specific regions or drivers on the loudspeakers.
3 no one wants to deal with a shorted out amp because wires were crossed or grounded to something somehow.

if you just like to see dangling active wires then cover them up with non conductive stuff as they are ‘live’ and a possible serious problem waiting to happen. kids, pets, vacuum cleaners, etc.

This is what I bought / use.

https://www.ebay.com/p/4-Pcs-Hi-end-Banana-Spade-Adapter-Plug-Speaker-Cable-Connector/1184934218?iid...

They work great, I switch between speakers with single posts and double (bi-wire) with ease and peace of mind.

Well worth the the money. 

I would just buy one pack of the attached.  On each speaker post you would use both one of the banana connectors already on your wire and also one spade from the banana to spade connector.
https://www.amazon.com/dp/B00X9FET7I/ref=sspa_dk_detail_1?psc=1&pd_rd_i=B00X9FET7I&pd_rd_w=y...

This is if you don't want to cut your speaker cable.

@ scott_w

I also agree with lowrider57

Something no one has mentioned, will the un-terminated ends of the bi-wire cable work as an antenna and introduce RF back into the output of the amplifier?

You might want to send a PM to almarg and ask for his thoughts.

Same question was asked last week - most binding posts will accept two bananas one in the bare wire hole, one in the banana hole
https://forum.audiogon.com/discussions/please-help-me-clean-up-this-stupid-speaker-cable-mistake/pos...

Thanks everyone! Good info. 

Rodman, understand your comment and knew it.  I was just trying to say it in layman's terms to give scott a better idea to build from.  Keep the biwires together.  You paid for all that wire.  Use it!