If you had enough room, Only other way is to put a Baro before the DV or get the DV adjusted correctly with a manometer.
You can try a Rehostat, but slowing down the exhaust gases is the same as closing off the adjustment. You CO could go off.!!
The inlet to the DV is very touchy as you already know. My plate on the inlet of the DV is about 1/2 closed, you can adjust the Combustion air a bit and it will affect the draft some, but without a manometer to actually monitor what is happening, you are just a taking a chance.