Is there any way you can modify it to use the "insert from URL" script step? The web scrape method is not limited to the string limit of URLs on windows, but you have to read the results out of code. A lot of people will set their web side to generate an XML file, which is easy to grab and parse in filemaker.
You *might* be able to scrape the data in a web viewer to get the contents back out, instead of passing it in a URL. I haven't tested this at all, but if the raw html contents also includes what your user types in, this could be possible.
You may have a look at the demo file posted in https://fmdev.filemaker.com/message/96083#96083