I get cold after a few hours in the stand too, seems there's nothing I can do, also I get a bit bored and need to walk around.
As mentioned, walk in with the heavy clothing open or off, don't want to sweat.
Loose layers- knees, toes and hands are my worst areas.
Do you have an old sleeping bag you could pack in or leave at the stand in a weatherproof container?
I always envied those with enclosed stands that could be heated but In my area things grow up too fast, get cut over or other conditions change to invest too much into one stand. A buddy has a camp on a river near me, no other camps for 2 km and they logged across the river leaving a 100' buffer between the river and the clearcut, forcing any passing animal near the river. He has a perfect 130 yd view to a little meadow- sit inside by the fire and wait- lol.