Discount for signing up for multiple events

Would love to give registrants a discount if they sign up for 4 workshops (events). This can be limited to one shopping cart - in other words, registrant signs up for all 4 workshops in one sitting, not by registering today for one workshop, registering tomorrow for another, etc.

For now I get around this by having an extra event for the series (category) that states "All 4 workshops in the series = discounted rate of $nnn.nn." The biggest drawback with this method is that they can't register for 3 workshops in one series and 1 in the next series.

I need this functionality as well - the ability to apply a discount when a multiple of specific events are registered for at once.

Thanks.