Poncho Liner or something similar. Don't put it under you.

Slip it between the UQ and Hammock. Gather up an end corner with some line, run the line through a hook on a bungee cord (works like the shock cords on the UQ) up around the whoopie sling and back to the other corner.

Should get you another 10 degrees.

I use just the poncho liner set up like that in late spring or early fall. Another Poncho liner for a TQ.