New Post: Does SPDisplayRelatedInfo Work With Normal Input Fields?

I'm trying to get SPDisplayRelatedInfo to work with a "Single Line Of Text" field, similar to here:-
http://sympmarc.com/2009/11/27/interesting-new-use-for-spdisplayrelatedinfo/

But it doesn't seem to be working. Is it supposed to? The comments in that link weren't clear.

Thanks.