I'm going to assume that when you submit your pick in the forums, you will need to post the position that the player was submitted in and not the position you may or may not intend to play that player (since you are required to pick one (and only one) of the non-OF positions, 3 OFers and 5 SPs, and 5 RPs, you can't pick another one that was submitted under that same position that would put you over the allowed limit.
Ex. Player A was submitted as a 2nd baseman but could also play SS. I draft that player on the intention on him playing SS but in the next round I shouldn't be able to draft yet another 2nd baseman (since this could possibly leave someone without a 2nd baseman).
Maybe it would be good to put up a table or something such that when people pick they see which positions are available on their teams (and everyone elses), how many players might be still looking for a certain position, etc. rather than just a list of picks.
[Edit] I'm just wary that people who pick players in the draft center might be unaware that they are picking multiple players from the same position pool and thus we'd have to point out when people make an illegal pick alot of the time.