[tex-live] Accessing fonts in LaTeX

[Gerben Wierda]

Suppose I have an .fd file with some special font like a light  
variant of the main font or an ultrablack. I can define these in an  
fd file

\DeclareFontShape{T1}{gwfoo}{s}{n} {<-> gwec-foodemibold}{}
\DeclareFontShape{T1}{gwbar}{l}{n} {<-> gwec-barlight}{}
\DeclareFontShape{T1}{gwopa}{u}{n} {<-> gwec-opaextrablack}{}

But how do I access these in LaTeX? There is no \textub{} command for  
exttra black.

Or: How could I create a sty file where one could have (for a rich  
family) a set of the light+demibold or the normal+extrablack as 'set'?

This is all doable in ConTeXt, but is it als doable in LaTeX?

G