gr7070,
I tried that first thing because there is access to the plunger and spring from the front like you mention. I used a small, thin screwdriver, but even with the plunger pressed in the base of the sight is too long to seat with the roll pin in place.  After I shoot it tomorrow I'll remove it and see how much trimming I'll need to do to the base of the sight to get it to fit like it should.

I take it that the same SDM sight (green one for you) snapped right in to your 627 with no problem?