actually you can. it doesnt work as well, but i just made some really good honey oil with 70% iso. my cousin smoked some last night and he said that he felt like he was on mushrooms! so you can! good luck
70% works but the extra resources invested in higher grade iso is much worth the time. You have the potential of making a lot of shitty oil with 70% but 91% offers a lot more for just a few more cents. And if you find 99% it would taste so good as well as get you that much higher.