I've done it with the hose clamp technique (and wood clamps and bottle jacks and prayer). I've also used this technique:
http://business.baylor.edu/Richard_Easley//autofaqs/tseals.htm but without the silicone sealer (sealers and oil passages make me nervous). In each case the grommet was dry for a while and then inevitably started weeping after a bit.
According to a friend who is a Mercedes tech., the only lower turbo drain seals that are dry are the ones that don't leak... YET.
In my shade tree mechanic mode, I push the grommet down in the top of the pan with a 3 ft. long 1x2 every few weeks and it's kept the underpan area the cleanest. Not elegant nor definitive, nor proferred as a solution