In the meantime, if I understand your question, the way I do it is to do the fit as you do.  Then go to the toolbar and click on "copy parameter" icon.  Then open two new fit pages (Fitting -> New Fit Page) in the first load the ellipsoid model and the second the MSA structure factor.  in each use the "paste parameter" icon to load the relevant parameters of your actual fit. Depending on your version you may need to adjust - for example in 4.01 scale is set to 1 in the P*S with vol fraction specified once.  Since there is no vol frac parameter in form factors currently scale will be one but should in fact be set to your volume fraction (of course).  The real annoyance is the effective radius in 4.01 which is NOT listed in the P*S but is calculated behind the scenes.  In other versions it does show up and I believe will in 4.1.  For a sphere is pretty easy .. for other shapes a bit more painful.

Anyway once that is done you will see M2 and M3 (or some other number if you've done other things) in the theory box (see the graphic Andrew sent).  just check both of those (and make sure all other data or theories are UNchecked of course) then sent to plot of the graph# that has your data and fit on it.  You should now have I think what you are looking for?  This part is what you will have to do also in 4.1.  The difference being you won't have to create the 2 fit pages to get here... or potentially have to deal with missing parameters :-)

Hope this helps

Paul