Empty cart AND redirect in same URL?

Hi everyone!

We're getting ready to go on-sale with a virtual workshop, which has 4 individual classes that people can either purchase a la carte or in bulk in a fixed package. We are planning to use message rules to identify when someone puts more than one of the a la carte events in their cart, encouraging them to go for the package instead. Here's where the trick is: we'd like to embed a hyperlink in the message rule that not only brings the patron to the package page, but ALSO empties their cart. 

I've tried appending the ?abandoncart=true tag to our package URL page as:   /packages/fixed/###?abandoncart=true -- this link brought us to the package page correctly but did not empty the cart.

I've also tried to start with the cart page and follow it with a redirect as:   /cart/details?abandoncart=true&ReturnUrl=%2Fpackages%2Ffixed%2F340  -- this link worked to empty the cart but did not bring us to the package page.

Has anyone else had success with TNEW links that empty the cart AND drop the patron off at a new page? I'm stumped!