Hm, I guess the only option is to put the washing machine on something. I spontaneously thought of a Euro pallet, since they are relatively sturdy and surely can absorb the vibrations during spinning well. But does the height fit?
Otherwise, solid boards (worktop?) might be suitable - a washing machine can weigh around 100 kg depending on the model, and the vibrations during spinning should not be underestimated.
Regards, A.