I understand how to make the implementation work initially, however I would tell the client no we don't support that, and then wait for them to offer an amount of money to make it worthwhile.
It's not hard, however, it complicates the software leading to subtle non-obvious bugs, and then you need to support this features with all the other features you're adding, etc.
PS. What happens when they turn if off? ...and then back on? And then the 20 other subtle bugs that this feature introduces... And how many other features that lots of customers want are we delaying while we implement this?
All this work for $24.95 a month... yeah... no, 86'd.
But remind me never to ever use BLOX. This seems like the MOST basic thing you'd want to be able to do.