I'm fairly certain that you can substitute a regular Shimano Hollowtech BB for that MegaEXO unit. That is if MegaEXO is MegaEXO across the FSA product line and there aren't two different standards.

I have and FSA Gossamer MegaExo Triple Crankset that I picked up at Nashbar last year and I simply substituted a Shimano Dura-ace BB-7900 68mm External Bottom Bracket that picked up on Amazon for a little over $20 when they were on sale. It fit right in, although it was a little snugger fit it wasn't bad. Pops right in with a rubber mallet no problemo. I'm using the MegaEXO BB on my CX beater with an old weird Sugino crankset that they only made a few of. It's Hollowtech compatible too.