Go buy some octane booster at autozone or walmart. It will bring 87 up to about 90, maybe 91 depending on the dilution ratio.

I dont know about the chemical effects of octane booster (besides the octane rating) so use at your own risk. But I brought 2 bottles with me to a cabin town where they had no premium gas. I didnt need it though so couldn't tell ya about the end result.