Why not try it, MK, and see what happens? Waxes like beeswax and candellia wax are great way to increase the melting point in a product, although they might stiffen the product more than you want and they can leave a waxier feeling on your skin, so a small amount like you suggest is a great idea. Candellia wax has a melting point of 70˚C, while beeswax melts at 50˚C to 55˚C, both of which are above the melting point of our butters.
EMULSIFIED SUGAR SCRUB
10% emulsifying wax (e-wax, Polawax, BTMS-50, BTMS-25 BTMS-225)
10% cetyl, cetearyl, or behenyl alcohol or stearic acid (5% cetyl and 5% stearic is very nice)
10% cocoa butter (or other really hard butter)
10% shea or mango butter (or quite soft butter - shea aloe would be great here)
1% Vitamin E (optional)
2% fragrance or essential oil (optional)
You can also substitute one butter for another, or use all cocoa butter instead of using a bit of shea butter. Cocoa butter with a melting point of 38˚C, mango butter at 34˚C to 38˚C, and shea butter at 31˚C to 37˚C. (Check out other butters in this post.) But remember that when you substitute a stiffer butter for a softer one, your product will feel stiffer and harder. (Yes, kiddies, that did sound rude!)
You could also increase the amount of stearic acid or cetyl alcohol in place of some oils. For instance, you could use another 10% cetyl alcohol in place of 10% of the liquid oils, which would increase the melting point of the product. It would be a bit stiffer and harder to get out of the container than one with less cetyl alcohol, but it would be less likely to melt. As well, you could consider using more emulsifier, which would also stiffen the product.
Something else to consider - keeping it in the fridge during the summer months. It's not a lot of work to get it out of the fridge before taking a shower or bath, and it means you can keep the wonderful skin feel and texture you've created in your product all year 'round!
Let us know what you do and how it turns out!