Question About PSP/PSN download titles...

Unsure if this is the correct section for this, if it isn't please move as appropriate.

I have PSP (slim model the 2000 one), its a PAL/EUR one as I live in the UK.

I made a US PSN account and purchased a US PSN points card...

When I installed the custom firmware, it unlocked/decrypted the Metal Slug DLC, so I could use it with my EU PSN purchased download of the actual game and can use it on my EU account.

I also bought the TurboGrafx game, Bonk's Adventure off the US PSN store, however this won't work when I set my console back to my EU account, is there any way around this?