Interference and normalizations

I am trying to build a PDF which takes into account three distribution in the form of RooHistPdfs. However, one of the densities is not actually a probability distribution since it arises from the interference of two amplitudes and can be negative. If I use RooAddPdf to build my model, each individual histogram will be normalized (I think), which does not make sense. However, I would like to turn off this feature and have just the sum of the three distributions be normalized.

Are there tools that exist for handling RooAbsPdfs which are not positive definite? Is it possible to have a RooAbsPdf which isn’t normalized?