Perhaps those that know for definite that they will be attending the AGM and standing for one of the seats may provide a letter saying nothing more than the fact they have the intention of standing for one of the directors positions although for now not to specify precisely which seat they maybe standing for. Final details can be finalised via the list. I would suggest that there be a deadline for which people need to finalise what role they want.
Could I also clarify that there will be 4 positions that will be required to be voted on? These positions are as follows: Treasurer, Chair, Secretary and lastly Membership.
My understanding is that you just stand for the board in general and then the positions are allocated at the first board meeting.