Isolating speakers from hardwood floors

"search engine" the forums for posts on Vibrapods: there have been several of them & some very recently. This might be very helpful for the scenario & they are quite inexpensive.
If cones are still desired try the BBC MK-2's; they have integral threaded locking levelers.

Sounds to me like the best thing you can possibly do is put Aurios Pros under the spikes. They give you almost all of the advantages of spiking, but float the speakers so there is some substantial limit on the floor-speaker interaction. They're expensive ($200 apiece, and you'll need eight), but worth it. You can check the website (Media Access or Vistek) or audionut.com. Good luck.

Use their regular supplied spikes placed on MDF 3/4" platform from nearest Home Depot. Place that platform either on the vibrapods that match excellent with hardwood floors or the bicycle tube.
If you want to go with the bicycle tube you'll need to get large staples to shape the tube for the platform contour and than just use a regular bicycle pump.

try sorbothane round isolation pads. work great with speakers and subs. have some on sale on audiogon. they can be stacked if necessary.

I have a similar problem to you (I have uneven wood floors on second floor), though I do not need to worry about noise. This cheap ($5) solution worked perfectly for me. I went to home depot and bought two round concrete stepping stones that you might ordinarily put in the garden. I also bought some small adhesive rubber feet to put underneath the stepping stones. I put the speakers (w/ spikes) on top of the stepping stones and immediatly got tighter bass response as well as less vibration/sound transferred to the wood floor. This raised the height of my speakers about 2.5 inches, but in my particular speaker (Monitor Audio 5i) this was desirable because they are small in stature and benefit from having the tweeter raised closer to ear level. My only complaint is that there are lots of little holes in the concrete, so sometimes it's hard to place the speakers, because one or more of the spikes slip into the holes. A granite slap, marble slab, or other non-pourous heavy material might do better. Just don't forget the rubber feet to keep the slab of whatever off the floor.

Good Luck,
Gil

Like the airman's advice. When I used to run monitors on spiked stands, I'd effectively couple them by resting them on 4" thick white-marble slabs I grabbed as broken sections off tombstone-manufacturing debris near a quarry in Vermont.
Now I have speakers (Verity Parsifal Encores) that WAY more expensively accomplish similar feats by floating a 1" thick granite slab between the bass modules and the upper monitors. but still using massive spikes down below.
Have fun!