You need not convince WCG... you need to convince your client, which has determined that it's -not yet- it's turn.

From a technical point of view, seem to remember if one selects WCG in the project tab, or ant other and hit update, it would fetch some work, but this could be a latest client feature. Blunt force, in that project tab suspend work fetching for the other projects, and WCG will start backfilling the buffer, outside of it being it's turn. Often proposed, WCG is really 7 projects under 1 umbrella, so you could consider giving it some more project weight / resource share.

Work is done block wise, so you see a client alternate, sometime one, sometimes the other more done, but in the long range the average is supposed to work out to 8/Nth (where Nth is the sum of all the weights you've set).