Hi Ariel

Re Solpart menu
Are you using an old skin or non current version of DNN? AFAIK the solpart menu is no longer used as is has many issues and is not very flexible - not so good for SEO either.
If you look at any current DNN skin such as MinimalExtropy you will see that nowadays DNN uses the much more useful and configurable dnnNAV.
It may well be possible to do what you wish with this control although I am unsure how this might be easily achieved.

When I have needed to have 2 menus on the same page I have simply bought a new menu that works as a skin object (like dddNav and Solpart) and can be used as a module.
I just add a target pane where I need the menu - add the menu module to the page and then use the menu's config page to tell the module to only display specific pages.

IMO: This is a very quick to implement solution and it also allows such nice touches as placing a module on child pages to list other pages in that menu group.
In such a scenario I usually use the menu as a skin object too for the main menus and do not use the supplied menu at all.
Most of these menus cost less than a couple of pizzas (and the beer to go with them).

Menus I have used that allow page exclusion include
SEOMenu CSS Menu
http://www.snowcovered.com/Snowcovered2/Default.aspx?tabid=242&PackageID=14901

CSS Side Menu
http://www.snowcovered.com/Snowcovered2/Default.aspx?tabid=242&PackageID=17304

The free and promising looking DDR Menu also lets you exclude menu nodes.
http://www.dnngarden.com/
A quick guide to stlying this menu I found while searching for the DDR site
http://www.dnncreative.com/Tutorials/SkinningTutorials/DNNGardenDDRMenu/tabid/595/Default.aspx

Hope this helps

Ian