I have always removed the drum to install the seal. As I wait for the glue to dry a bit I clean out the rest of the dryer. The glue is really tacky and should help hold things in place. I sometimes use a spring clamp or two to help me hold it in place. Somedays I'm in the zone and don't need to use any clamps, just get lucky sometimes I guess. Not sure what else to tell you, sorry.
Maybe another tech will have some words of advice for us.