I just did this and it works for the 2 games I tried so far... Little Big Planet and Ratchet and Clank - Crack in time.
LBP worked straight off and Ratchet said the game data was corrupt but it did work. I haven't earned a new trophy yet but all my old ones are there still.
As a little background I'll tell you what I did. I was on OFW 3.41 using my jailbreak. I did a total backup of my HDD using a file manager and using the backup/restore option in XMB. I put a totally fresh HDD in my PS3 and let it format. I tried a downgrade to 3.15 which failed (orig firmware was 3.40 so I expected this but I had to try
After all I got it to take 3.41 modified and then installed 3.41 OFW from the recovery menu. I went through backup/restore on the XMB again and restored my HDD fully except trophies. I think I lost Bluray and DVD as well (I checked my flash 3 and my CRL and DRL files are dated Dec 1979) will have to test further. EDIT - DVD works, I can only assume Bluray does too.
I restored my trophies using the instructions above, rebuilt the database and bammo my trophies look just like they did as before.
Also I did not lose my game saves when rebuilding but I backed them up just in case.
hope that helps.