I'll be very upfront with the advice I'm going to give. I have never roasted a geisha, as I'm too nervous I'd screw it up for the price I paid. Considering Red Beard had that one for 50% off, it was a good one to try (I'm guessing that's the one you bought).
My understanding with geisha (and there are a few others here that know what their talking about with this bean, so listen to them more than me), is they are going to require a slower roast with more development time. With a popper, given you don't have temperature control throughout the roast, that could be an issue.
Have you thought about using a long extension cord (50-100') to plug your popper in? The long cord causes voltage drop by the time the electric gets to the popper, therefore lengthening the roast time. A lot of people use extension cords on their poppers for some of the more delicate beans. That way they get to first crack around the 8 min mark, for instance, instead of say 6 mins.