Only from added mass. I don't think that a rubber plug in isolation would do much as it is not an intermediary between 2 different structures of differing rates..

As long as we are fantasizing: Between the drop outs & the axle would have an effect.

But in reality land: So would between the rim & the road, between the headset & the stem or the stem and the handlebars.

Or as added mass on the bar ends. Effectivly minimizing the distance x force moves the lever.