1) take a random save from your ps3 account from a game thats not copy protected
2) use the save you found that you plan to get trophies with
3) use xploder to copy over that save

Your theory is correct sir however the most common misconception with Xploder is people "think" you need 2 saves for ever game save so you can overwrite them. What people fail to realise is that its alot simpler then that, all you need is 1 save of yours to detect the account name. Then you drag as many saves as you want to the "Username" and Xploder does the rest. The only problem why this wouldnt work is if the game save your after is missing a file like the param.sfo for example which alot of people tend to take out. This was due to noob protecting the save early on for CFW users before Xploder took off.