I’ve seen both Silly Putty (which is silicone) used.
Also, saw someone use silicone caulk for abstract shapes.
I have also tried to master this challenge.
Since making a mold with silicone caulk is not very difficult or expensive, you could potentially make a mold with your object, place the object in the mold and pour resin on top. Or use the reusable mold material seen on resin obsession..
Without knowing what you plan to resin, don’t know if these ideas would solve your problem.
Good luck!