What is the (monetary) difference between a Freighter CN salary and Pax F/O?.
If it's negligible, a solution may be to right seat qualify the chaps on the MAN base to the 777 and wait until their seniority comes up for command.
If that is too heinous to contemplate, they could rotate half the chaps on a six monthly basis through the 777 in the right seat, or even dual qualify them - CN B744, F/O B777. There are already a number of pilots on the 3/F who are dual type qualified, so it's hardly precedent setting.
The issue of an underutilized workforce in MAN has not gone away. The company has given clear notice of it's intentions and the hammer IS going to fall, in due course.
The onus is on US to produce a solution - and present it, with it's productivity and pecuniary advantages - to CX to digest and eventually present as their own solution. (G*d forbid they actually acknowledge that their "million dollar morons" are capable of producing a working solution that actually SAVES money.)