Dynamic: Has the OP considered adding some weight to the push mower? A secondhand diving weight belt or similar may be enough to satisfy the requirements as long as looks are not important.
No, I haven't thought of that, but there's so little of the actual mower (mainly just a frame) that I might have trouble finding somewhere to put the weight!
Here's the one I bought, cost me $45 (was on special at the time, current price is $79). Only used it once, anyone want to buy it cheap?