Ghetto. Filling the mounts with single part urethane or silicone is ghetto. It takes a really long time to cure, and you're just filling the air cavities, not replacing the rubber itself. I'll laugh at you, and so will all your friends.
Buy some real mounts if you think you need mounts.

There is one other option:
Find a place that does mount filling with a core swap. I used to do that a few years ago; I made a set of molds each for Civic and Teg mounts. Carve out the stock rubber, drop the mount in the mold, and fill with 2 part urethane that is made for that purpose (motor and engine mounts, vibration snubbers, etc). I think I used shore D 80 or 85 durometer but I don't remember. I bought a set of mounts from a friend and started doing it on a core swap basis, so I give you a set of mounts and you give me your old ones, which I'd sandblast and paint. I don't do it anymore, because the urethane has a shelf life of a few months and has to be bought in minimum quantities of around 4 gallons at $150/gallon. I did some shore D 90 mounts too, which were a pretty orange urethane but would rip your fillings out. Pretty much race only, which is what I made them for (not for me, but for a few choice clients)..

Anyway, I seem to remember that there were some other people doing pretty much the same thing that I saw on the 'net in my travels.