mordent with a slash

[Robert T Wyatt]

If one played b c b as a triplet, then this is what I would call an 
inverted mordent and I would use a mordent with a slash through it.

Can I make this happen (2.5.23)?

I did find a reference that a prall is the same as an inverted mordent.
http://www.answers.com/mordent

The prall symbol in lilypond however is not a mordent with a slash 
through it:
http://lilypond.org/doc/v2.5/Documentation/user/out-www/lilypond/Articulations.html

Insights are appreciated.