There's no memory expansion modules that I'm aware of.
But there are some things you might be able to do to better use the memory you've got.
Check that you haven't created data tables that you aren't using in your program. Also make sure that all your data tables that your program uses are sized to just the length you are using, and no bigger. Open each data table and click the USAGE button. If there aren't 'X's, go to right-click on the last element and select CROSS-REFERENCE (to check for indirect addressing).
If you've laid out your data tables intelligently (instead of just grabbing any old address) you can take advantage of file commands (FAL, COP, FLL) instead of individual data manipulations (CPT, MOV).
You might even be able to do lots of repetative tasks in FOR-NEXT loops, using indirect addressing. These two techniques can reduce your program file word count quite a bit. They also make expansion easier, since you just have to increase the data table size and the length of the instruction and you're mostly done.
I've been just over full on a few projects, and had to resort to the following byte-finding techniques:
Sub-Branches with no conditions (like this
A
---+-------| |-------+---
| |
| B |
+---+---| |---+---+
| |
| C |
+---| |---+
Saves 2 words if just extended (like this
A
---+---| |---+---
| |
| B |
+---| |---+
| |
| C |
+---| |---+
You are eliminating one BST and one BND instruction.
A CLR N7:0 uses one word less than MOV 0 N7:0. Of course, even better is (like I said above) is when you can do FFL 0 #N7:0 10 to replace 10 instructions.
A word here, a byte there may not help much, but there are times when it just enough.
If you want, post your program (as a .zip), and I (or others) will look at it and suggest ways of trimming it.
Good luck!