I'd book two PNRs, call and have an agent split and link the PNRs. This will allow you to be placed on the UPGD list. When you are within your UPDG window, see if you any C+ seats are available. If so, call an agent and get them to assign your two seats in C+.

Note: If you end up getting upgraded BEFORE you are able to get a C+ seat, then you will NOT be able to out your companion in a C+ seat should one become available as you must be in the same CABIN for that benefit to extended.