Yes you do get bypass pay
In CoS 99, it states that unless you are Cat D you are entitled to bypass pay for any captain that is extended.
It doesn't matter if he is extended in C+T, or basing. I don't think he generates bypass pay if he extends on the freighter.
Interesting example...if the most senior FO is on a base (hence CoS08) he will NOT get bypass pay for any captain extending in hkg or base until they extend beyond 65! The second most senior FO, say in HKG on CoS99, does not inherit that bypass pay. FOr him to get it there needs to be a 2nd extendee.
All 50+ year old HKG based captains must be getting worried. If the bases have filled up they won't be able to get a base. And the ones on the base can work till 65 now. So the hkg based captains can only get extended if they go into C+T or fly freighters!
I wonder if that was the company's intent with this deal?