I think this is the track you need to pursue, so hang in there.
The changing of fonts when you print from Windows / IE will be effected by a combination of Windows, the printer driver for this printer, and IE. In the end, a few special ASCII characters will be shipped to the printer telling it to switch to "control font" and interpret the subsequent received characters as action directives instead of characters to print on the printer. Another control sequence will return to regular printing.
You really need to find this control character sequence. There must be a way to inspect the printer driver to see what it does to invoke fonts, but I am unaware of how to do so. So you need to rely on printing a very small Word file (that includes identifiable conventional text before and after the control font character) to a file and inspecting it with a hex editor is the way to determine the control character sequence used. (It sounds like you've done this already.) I can help you examine the file if you send it to me. Shame on Epson for not prividing the details!
When we figure out the sequence required, we can then play with making it happen in HTML.
