[Rivet] stacking or adding .aida files

[Lynn Marx]

Dear Rivet experts,

I found myself faced with what seems to be a fairly easy problem. I have two aida files which contain, say a plot of pT(Z), one file is for W{^+}Z and the other for W^{-}Z. Since those two have different cross-sections (for pp collisions) that I need to set in the jO I can't just run over all the samples with the total cross section as that would make the contributions weighted incorrectly.
If I then want to plot these as a single contribution, what I have done so far is added in my .dat file

Stack=WpZplot WmZplot

and set LineStyle=none for one of them so that it looks like there is only contribution. This works fine also if I still add a third curve, say from a different generator. The problem is however as soon as I need to Stack more than one pair, i.e. if I for example want to plot MCatNLO versus Powheg, then doing

Stack=MCatNLOWpZ MCatNLOWmZ
Stack=PowhegWpZ PowhegWmZ

gives me funny results.

Is there any work around to this? I could always resort to root, but I figured if I get a chance to not use root for once I might as well.

Cheers,
Lynn