Today I knocked out the other required ostrich tail and routed the corresponding groove in the skirt. At this point it was time to try a dry-fit to see if the "floating tongue" idea would work. Here's a picture that may give you a better idea of what's going on here:
I'm pleased to say that it appears that the floating tongue concept does work pretty well; the skirt did force the benchtop to be much flatter. However, it did require a lot of force to wrangle it into shape. After all, these are some thick pieces. Here's an "in progress."