Fruitless. :-/ I even dug up a guy from an 8 year old thread I found where he was talking about a solution for this but apparently whatever he had discovered at that time is broken (or fixed, I guess) in current Modo. So it's a no-go unless I can script something up myself. That will ... take awhile.
Just tried to script it. The issue is that regular weight maps are vertex maps, and the subdivision weight map is an edge map. So I can query the values from the subdiv weight map, and technically apply them to another weight map but it won't take because the weight map wants them applied to vertices, not edges.…