I have a thought that might be on the same idea, might not. Doesn't Omnicalc have a setting that enables you to have two calcs running at the same time, virtually? I've noticed that switching from one to the other simply freezes the first one. Although it would make them both slower, why not use the same idea and have both calcs get a variable ammount of execution time? It would let you do, say, long conversions in the background whilst designing something entirely different in the foreground.
Of course,this might not be what you had in mind...
I guess the ideal way to pull the thing off (although I have no real clue how to do this, this is just a thought) would be to have one program execute a line of commands (from one : to the next
and then have the second program execute a line, and so on back and forth. This would prevent any issues arising from both programs trying to access the same variables at the same time. Of course, it would be up to the writer of the individual programs to make sure the variables didn't interfere, unless that was their intention. (Or the graph or the screen for that matter.)
-gamefreak