At my mtn biking clinic they showed us how to do donkey kicks- but only those riding clipless could do it, because you kick your heels up,while clipped in, and that helps to kick the rear tire over an obstacle...
so you'd do a manual on the front, and donkey kick over the back...
they told those of us using platforms we couldn't do it.

Interesting enough- one woman who tried it donkey kicked so hard she went right over the bars...luckily she wasn't going too fast and landed on grass!!

and-
I'm thinking of going clipless now myself- I have WAY too many gouges on the back of my legs from those stupid pins on the platforms!
I ordered a pair of Ritchey V3 mountain bike pedals...they're supposed to be a bit wider, and clear mud well, so hopefully they'll be okay.

Kimba