Using a center speaker as only surround speaker?

I would like to know how detrimental it would be to my HT listening experience if I placed a Sonus Faber Piccolo (bi-wireable) center as my only surround speaker. The other bad news is that it would go on the middle back wall above my couch.

Reason for this madness - I want to timbre match my Sonus faber fronts (Concertinos-L&R and Piccolo Solo- C) I cannot get my hands on the "Wall" model and cannot afford a pair 2nd pair of Concertinos at this time.

I am sure there are a hundred problem areas, but any input would be deeply appreciated.
Surround ony add a little ambience. Yes you can do what you want, it will not be bad at all.
The rear surround only carry about 5% (to 10% at most)of the signal.
Go for it. Timbre matching will do you well. If that's all you can do for placement then don't think twice and enjoy!
Is your couch against the back wall?

Also, are you planning to just connect L or R rear channel?
The couch is against the backwall - I am hoping position the center on its back or angled up at the ceiling may create a better surround effect.

I was planning on just L or R and tell the receiver (pioneer elite vsx-29tx) that only one speaker is connected.

Any tips or experiments would be appreciated
I doubt that you will be able to select just one rear speaker, probably a pair or none, therefore you could use this device,

to send both L & R into a single speaker. Also, you have the right idea to direct the speaker toward the ceiling. This should give you a better effect than facing forward.
IME of setting up hundreds of surround systems where the couch is against the back wall it is very difficult to render the rear channel properly. The compromise that I found best was to pull the couch out from the wall just enough to put the rears on there back on the floor pointing straight up.
Ok - I will do some experimenting. I think flat on the back on the floor is going to be my first test.

I am pretty sure I can select just one speaker for the rears - I am using an old pioneer elite vsx-29tx, but thanks for letting me know in case I am wrong.