Hi, Aaron & Mark.
Another approach, which works for me, is to use the existing "£v" mechanism with WEB_ESCAPE_LEN set to 5, to allow five-character strings [and don't forget to modify all of the web pages that came with uTasker].
In a static web page, say Z.htm, I put a string of £vX£Y for the various Y values I want to access with my XMLHttpRequest document, doc using doc.open("GET",Z.htm?...params...,false). The X following £v is a character not already in use that I've programmed to cause fnInsertString() to access fnInsertMyString() that I've written. It substitutes the second £ with a value passed in by the parameters of the doc.open() request. Based on that result, it chooses which values to return. Since the web pages themselves are static, there is no need to worry about wearing out FLASH.
One thing -- very important -- to prevent various browsers from reusing previous, cached values, I've found it necessary to append the current time to the doc.open("GET",...) parameters. Some browsers can be convinced not to cache results, but this is the only way I've found to force all browsers that I've tried to use new data passed back. The downside is that the cache is being filled with old values that won't ever be reused. I think this applies to all AJAX programs. If I'm wrong, or if someone knows a better way to accomplish this, please let me know!