End special price when inventory drops to a certain level

We frequently use special prices to reduce stockholdings of slow moving lines - but to keep breadth of range we don't necessarily want to sell every single unit of these lines. We like to keep maybe 2 or 3 units, at the usual price.

At the moment we have to manually monitor stockholdings on these lines and take them off special price when the stock gets to the desired level.

If there were an option to end a special price at a particular inventory level (as an alternative to ending at a specific date) this could become a set-and-forget exercise which would make our lives a lot easier.