I don’t know if it is possible, the reasons for it.
At least prior to Win7.
When EmEditor is foreground, you see the Full FilePath in the titlebar.
When EmEditor is background, when you look at the TaskBar items, you can see a nice short filename-only readable text. Whereas if it was still full path you would only be able to see useless information at the beginning of the path:
e.g. “C:UsersFoobar…”

As far as comparing two files side by side, and keeping the “Path in the TitleBar” try this:
1) Menu: Window | Split
2) Drag the 4-arrow mouse pointer down to the statusbar, splitting your screen into half (and click once). Both sides of your screen now contain the current file, and both are able to be in different places of the file.

Take note, you can have up to 4 views of the file, or you can make the 2-way split horizontal instead of vertical by bringing the pointer over to the side of the Window & Left Clicking.