Larry,
I purged my wheel bearings a couple of months ago. It is a simple, straight-forward job. Just plug the grease gun onto the dzerk fitting and pump. The old grease flows out at you (around bearing on fitting side of wheel). Just keep pumping until it flows clear n' clean. It's certainly easier than removing the wheel(s) and lubricating bearings the old-fashioned way; that is, a gob of grease on the palm of yer hand and tediously tamping the bearing to force grease thru!
Can't respond to blowing out the seals - but, the method has been around for some time. All large aircraft I've worked with use some form of purging.
The grease needed for two wheels will probaly empty a standard size grease gun. That's a lot of grease. You'll be impressed at how black and sludgy(?) the old grease is. My trailer was just over a yr old, and "greasing wheel bearings" is now on my annual TODO list.
Denny_A