Any ideas on a way to add a vac pressure release somehow? Is there
anything made for something like this that doesn't cost an arm and a
leg?

I thought of actually adding yet another hole and dust port, and some
sort of Y- or T-fitting. So when one hole is covered, the other is
open. Problem is, that would start to add quite a bit of "crap" under
the table that I don't know if I have room for.

Have you considered drilling another hole in the top of the table, directly
left of the router bit.
Keeping the centerlines matched up. Once the board with the dado passes
over it that should
allow air to flow thru, thus releasing the

One note though, I've noticed that when cutting dados with a 1/4 straight
bit it does
tend to leave the saw dust packed in pretty, usually need a screwdriver to
clean it out.
Maybe, consider a spiral cut bit also.

Ron