Only If
If this movie had done well enough to get a sequel, here's my ideas:
The scientists rebuild the laser spectroscope, which leaves Howard w/ the choice of whether or not to return to Duckworld. However, upon a test, a human gets sent there, instead. How would he fare on a world where everything is too small?
_OR_
Duckword is, more-or-less, a parody of Earth (e.g. popular media, place names, etc.). So, what if scientists, there, built a similar machine, made accidental contact w/ Earth & pulled a human in?