The GOP shouldn't have complete control over the next redistricting, which hopefully means we won't get a montrosity like the current map, and Gerlach can be taken out much easier.
I don't know what the dems could do...a) They don't control the state house, neither chamber...b) there arent many dem wards they could add to PA 06 without severely weakening their hold on adjacent districts, and if they could add parts of PA 07 or 13, those districts might be the marginally republican (but less populated) wards. They might be better off, if they took control, to make that a safe GOP seat until demographics change and consolidate their gains in PA 07, PA 08...
Its actually quite easy. Look to PA-16. Lois Herr did quite well actually for a no-name opponent, particularly in the Berks and Chester county portions of those districts. Herr got 45% in the Chester county portion of the district. Chester went like 52/48 for Bush. And the more GOP portions of Chester County seem to be in the Gerlach district based on his showing.
I'd take PA-16 out of Chester and Berks counties entirely. I'd make PA-07 a Delaware/Chester county only district. Though the district would probably be a 51/49 district, Sestak should be able to hold it easy and by the time he moves on, it will likely be even more Dem leaning.
I would then take the strongly Dem portions of Montgomery County in PA-07 and add them to PA-06. I'd also add the Dem-leaning portions of PA-16 in Berks County to PA-06. I would shrink the Berks County portion of PA-06. Meanwhile, PA-13 can come out of NE Philly a little to allow for population gain in the two philly based districts.
This plan also would make it really easy to combine PA-16 and PA-19 to allow for the elimination of a district.