I will give you my experience. You will have to decide if it is worth the risk. I would suggest you test it on a spare body. I have read of others using Silly Putty. Appears to be somewhat popular with the military folks. I was at a dollar store and found a pack of knock-off Silly Putty. I have no idea of the brand. I used it on vents on a race car. I placed it on the unprimed, unpainted outside of the body shell to keep the flat black that I was painting on the inside from coming through. There was also a crazy shaped hole for venting that I had no idea how to mask. I had absolutely no problems with the knock-off Silly Putty sticking nor did I have trouble with final paint. I will tell you that I wash my models throughout the sanding and painting process. I would not discount what other have said, maybe I was just lucky. I will say that I have used this putty on multiple models with no problems.
I hope this helps you. Good luck and let us know what you did and how it turned out. You may be a big help to the next guy!