Blocking Domain Access but allowing sub-directories of that domain? i.e. Reddit

Hey all,

Being a school board, I block Reddit due to the amount of nasty stuff to be found, but there are some sub-reddits that are useful and I would like to permit.  Is there any way to allow this?  I have it blocked right now in a custom category under the Web Filter Overrides, but have tried to add the desired URL  (for example:  reddit.com/r/science )  to the desired web filter, but does not seem to work.  Unsure the optimal way to handle this overall.