Is there a simple way to make the DS switch display screens?

See topic title.

I know of a few homebrew programs (such as Lameboy) that have an option to switch the display screens (so that the top screen displays what the bottom screen used to, and the bottom screen displays what the top screen used to).

Is this a simple method, or is it very complex?

If it's simple, can someone hack Lockjaw (http://www.pineight.com/lj/) so that either
- the top screen never displays anything and the bottom screen displays everything
or
- pressing a button...

Is there a simple way to make the DS switch display screens?