Return value to rule/ruleset Invoker

I have a use case where a rule is evaluated and the result has to be returned to invoker (a kind of return value action)
Does rules design support returning values to invoker ?

Here is a concrete example (actually trying to write some ubercart integration) :
I have a product that can be added to (uber) cart only if a rule is met :
- I created an event 'An item is being added to the cart'. + a few conditions (like cart contains product x)
- I invoke this event inside my implementation of the cart_add_item hook from uc_cart. When implementing this hook you should return TRUE or FALSE to tell uc_cart if it can/must-not add the product to the cart.

What i want to say is that there is no callback in this scenerio and you have to return a value while your on the stack. Check it out here for more info