For modifying the bus, ask the manufacturer. Maybe also ask the manufacturer why they didn't include a way to bond the can to the grounded conductor bus. Maybe there's a kit you're missing.
On the larger question, I've never had to deal with something like this, but it strikes me as wrong if they're calling it an MBJ. An MBJ goes at the service disconnecting means, no where else. A CT can doesn't sound like the service disconnect location. If this is ahead of the service disconnecting means then perhaps it's just a bonding jumper to the enclosure. One option might be to bring a bonding jumper from a point ahead or behind of the CT enclosure where you do have a grounded conductor lug or can install one. In that case you don't have to modify any of the current carrying busses.