How do I request an XML file depending on a variable?

Hello!

Long story short, I'm making a dialogue-heavy game in construct 2 using xml files, and I'd like to use the request project file AJAX option in a manner that'd allow quickly switching which file to load.

Problem is, in Construct 2, selecting which file to load is a drowndown menu (as shown below, left), so the conundrum is I'm trying to make it like on the right instead, to explain it in a single picture (FileToLoad being a local text variable).

Obviously I can't just edit the menus like in this photomontage of how I wish it worked, so how should I go to build around it?

Use "AJAX Request URL" action.

Just put the name of the project file in the URL field.