I wholeheartedly agree with Tom Winter:
a pulldump is no evil if maintained properly, just like most gear. I have not have one fail on me, and this is the 20th anniversary of me scubadiving. Although I have to say in all fairness that in the first 5 years or so I didn't use a pull dump, as I didn't use a BCD at all. But I guess that's not DIR at all, or maybe super-Hogarthian?
To answer the initial question:
It is possible to use a pulldump at the center of the wing.
I have a DSS wing with a (DR?) pulldump, and it works fine.
It is a tight fit though - one has to position the wing accordingly.
And the pulldump will touch the 1st stage slightly, especially when inflated. But I found this to be no problem, it in fact supports the dump when pulled, so less stress is put on the bladder.
The reason I personally like pulldumps is that I almost always carry a camera rig, and regularly totally empty/reinflate the BCD to lay down on the ground. I found it to be much more comfortable to just grab and pull, rather than hold the valve overhead or stick my butt up.
If I did cave or wreck diving I would consider going for an elbow though, as the snag hazard is real
Just my 0.02$$$
d-s-f