HistFactory Likelihood - constraint on bkg normalization?

Hi,

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:

JES

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:
Norm

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.

Xiaowen