Just a theory*
IF:
*PS3a = FW 3.41
*PS3b = FW 3.50
If someone with any *PS3a that is jailbroke can backup patch on to usb, Then restore on *PS3b that is not jailbroke via usb. You are saying this works. And they are obviously 2 different PS3's.
Then in THEORY could someone do whats needed on *PS3a upload there usb backup contents from *PS3a. Then some one copys all data on to formatted usb device and restore on their *PS3b. The journey of the files is effectively the same.
If you have 2 PS3's its going:
*PS3a > USB > *PS3b
If you download and only have *PS3b its going:
*PS3a > USB > PC(uploaded) > PC(downloaded) > USB > *PS3b
Or possibly someone backup *PS3a contents then sell usb device to person who only has *PS3b (effectively like having 2 PS3's)
Im not sure if this is possible. But it may be worth a try ?
If not then sorry