A script result can return multiple lines, which you could then parse out.
You can also declare global variables, using the Let () function and a positive calculation result. You'd have to know what they were, and remember to clear them after using.
You could also use If steps to set the result to one of many possible.
Passing named value pairs as script parameters is so useful, it should be built in to FileMaker. As you say, it's not all that straightforward to implement, but once you've put it in place it's fairly easy to use. If you're interested:
Both ideas are useful. Fitch, I'm bookmarking that website :) Those multiple param scripts look great for passing various field values for 1 record. In my case though I am collecting a list of scheduled payment records that I need to re-calculate so parsing multiple lines as Fenton suggest would probably make more sense.
For example, my database creates records for monthly payments. I want to build a list of PaymentID's that I need to update with new totals.
I've actually now found a solution using several freeze window / perform find commands in a script. That seems a bit clunky but I can now see how having a few regular function for parsing strings and list will come in handy.