Restricting values in a dropdown without javascript

[DominicRoberge2]

Hello

I am creating a survey for volunteers to register for a specific event. The event has multiple days, multiple time slots and multiple positions per time slots. I was able to use cascading select to get all that working fine, the only thing remaining is to LIMIT the number of volunteers to register for a specific job.  and because the survey will be public, I can't use a JavaScript function... 

My question is: Once 2 volunteers register for that task below, how can that job NOT be available in my position dropdown?

DAY,          TIME SLOT                  JOB                               MAX VOL NEEDED

July 29,     6:00 PM-10:00PM,     Overnight Security,                  2

this is what I could use as a lookup table:

Any help would be much appreciated.

Thanks!