The custom graph dialog editor only has 6 slots for variables. To show more you will need to edit the .vgd file directly (not supported in PLE or PLE Plus). See Chapter 15 of the reference manual for details.
Alternatively simply select all the variables you want to see and use the graph tool on the toolbar.
I am afraid I didn't understand you question, but you can put variables together in a view using the Shadow Variable tool which might be easier than editing the .vgd file directly.
To edit the .vgd on the graphs tab of the control panel click Save>As then use a text editor you like (Vensim's if you like) and modify the file according to the rules in Chap 15 of the Reference Manual). - Again only for Pro/DSS.