When I use a program such as xdotools or equivalents, to simulate keyboard inputs, ibus, and any IME ibus is hosting, seems to completely and totally ignore them. Tools such as xbindkeys can still interrupt a keypress from reaching ibus, but it can't then replace it with a different one.
There may be a program that can do this correctly with ibus, but the interaction isn't indexed by google, and I tried a few with no luck.