Yes. With the new Fakemeta module this could indeed be possible, doing it the way PM explained.
Pseudo-plugin (might work, might not, might create overhead):
Code:
#include <amxmodx>
#include <fakemeta>
#include <engine>
public forward_playerprethink(id) {
entity_set_int(id, EV_INT_button, entity_get_int(id, EV_INT_button) & ~(IN_JUMP | IN_DUCK))
}
public plugin_init() {
register_plugin("No crouching tiger, no jumping dragon", "0.1", "GWB")
register_forward(FM_PlayerPreThink, "forward_playerprethink")
}