i replaced the seals on my 97 vert top today and those of you that have done this know what a pain it is to get that lip to sit in the channel. i didnt want to use a flat head to push it in and risk putting it thru the new seal. i was sitting there having a beer when it hit me i used one of those plastic roller tools used for replacing screens in there frame rolled down the lip and it pushed it right into place. fyi dont use the metal roller ive seen them slice screens and fingers so only try this with the plastic ones

 

I don't have a convertible, but I have used a paint stir stick to help push door seals into their channels before. I just sand the end of it smooth, and go slow.

But, I like your idea better. With the plastic roller used to replace screens, you can just roll your way along the edge of the seal. The next time I am replacing door seals, I will give it a try.

Thanks for the tip.