When I molded PDMS, I used acrylic enamel over my photoresist mold and,
after curing the PDMS, dunked the whole thing into ice water. PDMS peeled
right off. Water swells the PDMS and the cold contracts the mold.

You could also use gelatin as a release layer or, my personal favorite,
cake icing. The cake icing remains gel-like until baked at about 150C for
~ 8 minutes (like baking cookies). You can then use hot water to dissolve
or bake at ~ 200C to carbonize the icing. To get a uniform coat of icing,
dilute it with water (it's only sugar, starch and coloring). Plus if you
get hungry, you can have a quick snack.

Mike