How to get xdotool to send simultaneous keypresses at precisely the same time?

I'm playing tekken on pc, and my keyboard unfortunately has a limit to how many keys can be pressed. So I'm trying to fix this by using xbindkeys and xdotool to map the combinations to a key press. This works unless the combination calls for pressing more than one key at a time, and I think this is because there is a very slight delay between consecutive keydowns.

For example, in 'keydown i keydown j' I will be pressed before j. Is there a way to let xdotool know that I want these to be pressed at the same time?