I had the same situation as you before I found a way to do it though, all you need is to download the patch normally from the PS3 thats 3.50 (in your case the slim) then data transfer it to the broken disc drive one (the 3.41 one). Then once its done boot up FTP server (on the 3.41 PS3) then change out the patch_mp.ff with a modified one and data transfer back to the 3.50 PS3. Hope this helped
Ohh and by the way the PS3 i used that was broken has now YLODed, what is this hair dryer fix you speak of? Any advice appreciated, I really need to fix it and if i can with a hair dryer rather then pay someone I would be very grateful. Thanks in advance