How bad is the vibration?
Is it low level, or is it fierce and actually shakes the hell out your arms as the latter will be dangerous on the dyno.
That said even low level vibration is going to affect your dyno run, spend a few £s and get it sorted.
I have no doubt that if the tyre place is reputable they will do it for free, it could be something as simple as the weight coming off as you drove away.