It's usually better to assign Joint constraints instead of using stiff links or dummy rigid beams with zero weight. That way you don't have to worry about numerical instabilities which may crop up if you use too stiff of a beam or link.

Draw a joint where you want to assign your load and/or mass, then select the joint along with the joint(s) you want to connect to, and Assign a joint constraint. Probably Body type constraint. In SAP you can convert any load cases into mass

I am not able to make it work. Attaching additional mass doesn't seem to make a difference. Any idea what I am doing wrong. I tried changing the mass source definition - no change. Thanks for your help.

Continuing my question: Does the 'add additional mass to node' feature actually apply to static analysis or only dynamic analysis?

Coulomb, in response to your last question, if you assign additional mass, the mass applies only to dynamic analysis. If you have SAP version 8, 9, or 10, why not draw a special joint on or offset from your frame, assign a load to it, then use mass definitions to convert your loads to mass?

If you are not doing dynamic analysis, you simply input the load as a joint force. Do you want to apply your load/mass along the length of the frame? If so, then draw the special joint on the frame. If the load/mass is offset, then draw the joint in space offset from where you want to connect, then assign joint constraints. If you draw special joints in space, you can draw anywhere, then right click joint to modify x,y,z coordinates