Dmitry offered this BlogJet tip as a comment on my technical blogging post:

Just a small tip:
to configure the format for "BlogJet This!" button, you can edit
<BlogJet Folder>\Data\Templates\blogthis.htm

Use this variables among your own formatting:
{$ .URL $} - URL of page in IE
{$ .Title $} - title of the page in IE
{$ .Text $} - selected text in browser.

This sounds like just what I was asking for...