Ok, worked out a solution. It's specific to my application, but maybe someone else will get something out of it. What I did is moved the calculation script from the field I am changing the access parameter of (call it "Field A") to the fields that feed into that field (call them "Field B" and "Field C"). Now, when the user triggers the exit events on B and C, each one fires a script that updates the value of A. For my application, this works only because B and C are hidden from the use if they toggle the radio button allowing them to manually enter A.
Basically, instead of A pulling values from B and C to calculate it's value, B and C check each other and push values to A.