There's some overlap in Professions, and it'd be nice to have a model in the rules for such cases. For example, there's a nice amount of overlap between spy skills and criminal skills; they involve many of the same things.
My proposal for handling it is simple, but I'd like critiques, etc: You can spend reserves from the secondary profession on rolls using the primary at a 2:1 rate, so long as the secondary skill is at least half the value of the first.
Although I suppose this is really just a way to use secondary skills in a situation…
For instance, if you were trying to hack a modern day computer, you'd use Programmer and Cognitech, right? But if you had infiltrated the computer with nanites, you can use them to perform some hardware bypasses; so you get to use "Nanotech Engineering" as a secondary to boost your available reserve.