Mowcius, your link showed an elastic polymer with resistance dependant on it's stress. Metals already do this, this is how blood pressure tranducers work in theatre. I can't see what advantage they have over a metal wire, but it would suffice. Are they expensive?
Well I was guessing without knowing the application - it would not be suitable for what you're wanting to do.
A two part silicone rubber mixed with fine iron filings or similar sounds like the best way to go - I don't have any experience with this though so I can't advise.