is_tree() function quirk

Good afternoon, my question is quite straight-forward.

I am using Widget Logic to control my widgets. As part of the conditions, I’m using an is_tree() function that is defined in functions.php of my main theme (using a child theme for Hybrid).

When WPTouch takes over and uses the Bauhaus theme, Widget Logic gets upset because it can no longer find is_tree().

I’ve been resolving this manually by adding is_tree() to the WPTouch theme’s functions.php file every time that I upgrade. But this is getting tedious.

Is there a way that I can register the function is_tree() for use across my themes that doesn’t involve writing a plugin?

Thank you.

http://ww.wp.xz.cn/plugins/wptouch/