It says you might be able to mix vix vapo rub, tooth paste and water....
I don't know how trust worthy it would be though. I would caution on the very high side if your serious about doing it....and if you do it - try to keep it on the CPU heat spreader and DO NOT spill any on the sides.
I might get bashed for telling you all this...so take it all with a grain of salt. IMO I wouldn't even try and make my own thermal paste and would not consider it safe to do so.
there was a thread a little while ago showing thermal paste substitutions. They tested mayonnaise, mustard, toothpaste, peanut butter along with other household ingredients. Its not advisable since good thermal paste is only a few dollars.