That's definitely possible. I believe you can accomplish this with a cross-table join. However a blend could work for you as well.
Here are two articles explaining joins and blends in Tableau in a lot more detail than I can cover in this single post:
If you have any questions about either though, let me know.
Thanks for suggestion, but as I'm charting the same measure from both tables a blend won't work for me (at least I don't think it will).
I've managed to find a solution via the Outer Join method. It requires a fair bit of formulas once there but it's manageable at least.