Freezing to the launch rail...
...or rod, or whatever you're sliding along, just to avoid arguments.
I've just suggested this in the last SPB article, but now there's a proper forum for dissecting ideas:
What about using chemical heat pack powder inside a hollow launch guide? The powder will get "up to" 45C according to most heat pack instructions, though the instructions also tend to state "do not disassemble". The ingredients are rust, activated charcoal and water anyway though, so hardly a major risk.
How much thermal expansion the rig will go through can be tested on the ground with a frozen sleeve and heated launch guide. The heat packs are good for anything between 8 and 24 hours when used as sold, depending on what pack you buy. I've noticed the 24 hour ones will take maybe an hour to get to full temperature though.
I did also suggest using resistive wire to make heat, but the various modes of failure plus a honking great battery to melt ice over a 5 or 10 minute period would probably make the chemical powder idea better.