Board Thread:Support Requests - Getting Technical/@comment-24957236-20140622160826/@comment-856287-20140622214123

Basically, you can't.

It's possible, but probably breaks the customization policy (you're not supposed to change the way the main navigation functions).

If you need more space on the main navigation, try linking to category pages as a portal to even more pages instead. Like instead of listing 32 items in a game in the main navigation, just use one link to Category:Items, where they will all be listed.