Craig,

This sounds dumb, but it worked really well.

I have a few of those 1/2" NPT flanges (threaded hole in the middle and meant to anchor pipe to a flat surface)

I screwed a 6" pipe nipple into it, then screwed a cap onto the other end. Took it to the grinder and ground the diameter down about 1/8" or so - didn't take too long. It was the perfect diameter for driving the seals in without damage.

Of course, after I did this, Rugo finds his Lisle Bearing and Seal Driver kit he bought special for this task - too late, it is still in the package.