It's on my wish list. Callable functions in the BIAL layer!
I've got a utility component that I can try to post next week that execute a section of BIAL script by setting a property that triggers an event which in effect executes the code in the "onChange" BIAL code, so basically it's a reusable function.
I've got another one that will do datatype conversions (instead of using Convert). Mine won't throw exceptions if you have a bad character in it, like Convert, does.
Still hoping SAP lets scripters be scripters and relax some of this sandboxed BIAL syntax. We shouldn't need to do all this.