HistFactory Likelihood - constraint on bkg normalization?


In the manual for HistFactory Likelihood (the hist2workspace tool), it says the likelihood is of the following term:
\prod_m Pois(n_m|\nu_m) * G(L_0|L, \Delta{L}) * \prod_i N(a_i|\alpha_i,1)
I know that a constraint is put on the luminosity. One can also put constraints on the nuisance parameters for systematics. For example:


The questions is, say if the normalization of a background (lumicross sectionefficiency) is measured elsewhere, and I want to use the result to constrain the bkg normalization. Is it possible to add a constraint term for that, and how? Can I do something like:

If it is not possible to do this with the hist2workspace tool, is it possible to add the constraint by hand to the RooWorkspace, and how?

Thanks in advance.