just put a limit on the players max yvelocity, and remember to add an if inthere somewhere to remove that limit when jumping of the bouncy things.
so like
if (bounce == 0)
{
if(yvelocity < -10)
{
yvelocity = -10;
}
}
then on collision with bouncy thing
bounce = 1;
and on collision with normal ground
bounce = 0;
somthing along those lines should work i think