Possibly, but there's no obligation (or real incentive) for the prospective cowriter to give you their share of the publishing. Again, once you give writing credit, you have given away property. In that scenario, if I'm the co-writer, there's no way I'd give you my publishing. The way the royalty structure on a song works, half of the revenue is the writer share and the other half is the publishing share. So on a 50/50 co-write, each writer's royalties are 25% of the total, the other 25% being the publishing share.
Asking someone to give you their publishing is asking them to relinquish half of their potential income. No way in hell I would do that.
Again, and I say this very respectfully....you're trying to be very kind and generous in a business setting - that's rarely a good move. It's called the music business, not music benevolence.
As I read what I've responded with to you, I recognize that some of it may come across as harsh or greedy....but when art and commerce intersect, it's a pretty big collision. For years and years, I had to swallow bitter pill after bitter pill because songwriters are, and always have been, the lowest rung on the music business ladder and consequently get stepped on the most. I've seen a lot of peers and friends make really bad business decisions that effected them for the rest of their lives. Perhaps I err too much on the side of "keeping what's yours", but it's because of how many repeated times I've seen songwriters duped in business dealings because it's our nature to consider what we do "art", when everyone else in the business views what we do as "commerce".

http://www.rogerbrownsongs.com
http://www.nashvillesongwriters.com/roger-brown