Use RooFormulaVar in RooAbsPdf

I have some RooFormulaVar objects I wish to use in a RooAbsPdf. Passing RooFormularVar
names in place of RooRealVar names in arguments works in RooGaussian etc, but not in formula expressions such as in RooGenericPdf (Error in RooFormula::Compile: Bad numerical expression) or RooAddPdf.

Using RooAbsPdf names apparently works in RooFormulaVar forumla expression, but not the other way round. Can anyone point me to a method for constructing a new RooAbsPdf using RooFormulaVar objects?

Just to add, is there not even a feature to access RooAbsPdf names in the RooGenericPdf formula expressions?