Jumping "on" and "standing on" are really different; you can detect the shaking/impact. Just standing on something implies measuring the strain/deformation on an object... like a bathroom weight scale.
Impact is straight-forward using an inexpensive knock sensor.
Accelerometers may be feasible if sufficient displayment occurs when step-on.
You could explore RF frequency shift such that a piece of copper foil/circuit board would be the antenna. Basic Theremin concept.
You could explore using stiff spring switch(es) on the bottom of the brick such that the switch is connected when weight is applied... like an inverted foot-switch.
Sensor list resource:
https://www.thegeekpub.com/wiki/list-of-arduino-sensors-and-modules/