Miele Man

I just put a pair of Servizio Corse tubular tire onto the rims. Unfortunately the rear tire isn't sitting quite right at the valve stem and thus there's a bit of a bump every revolution. What's t he easiest way to get the tire to sit on t he rim perfectly round. I haven't applied the tape yet because 1. I was wanting to stretch the tire prior to doing that and 2. I wanted to be sure the tire was perfectly round on the rim.

Thanks and cheers