Use a text editor such as notepad to edit the "'tumblebugs.xml" file in the "\my games\tumblebugs\media" directory. Locate the following entry on line 88 and change the value to 250.

[pathbonuspushertohead value="75"/]
Then, locate the following entry on line 89 and change the value to 100.

[pathbonusheadtoexit value="30"/]

Those values affect the bonus points at the end of the level give just after you splat the pusher bug; and from the location of the last bug to the hole.