I wouldn't suggest a rule for this. I would more make a suggestion and a detailed description of a possible addon that dead could possible make. In this addon it would add to the /coinflip cammond. It would open some sort of user interface that would allow the users to pick and choose what items/cash from there inventory they would like to coinflip. They would both go into some sort of lets say "box" on each of the users screen. along with this it would give you the option to eaither "flip a coin" or RDG a number.
You would also be able to change such outcomes as "lowest/highest" "number of turns(ft3, ft4,ft5 ETC).

TLDR
A btec cs;go gambling site. with features/functions