it's possible! i got them for most of my playthroughs but on occasion when i picked different options such as speaking up and being less quiet, i got different mentors.
For anyone wondering, which mentor you get seems to depend entirely on your dialogue options with Quirinus, except the dialogue choice that gives you a stat gain. My first playthrough I got Cenric and decided to start over, since Cenric didn't fit with the stats I want to focus on. My next playthrough, I kept everything the same except for what I said (or didn't say) to Quirinus, and that time I got Varyn, who I was hoping to get.
For those wondering, the conversation and stat choices don't affect who your mentor is, it is based off of who you ride with to the spire, the rest are purely just stats and special dialogue for who you ride with.
