3 keys on 1 button

I want to apply 3 keys on 1 button, so that when I press the button it outputs the 3 keys as being held until I release the button. If it's not possible to do this with 3, 2 would be fine too. Is this possible, and if so, how can I do it? I tried the following:

• Pressing multiple keys in the keyboard function section, but this doesn't work.
• Doing it with macros, but I don't get the effect I want. It either releases it in between the different triggers, or infinitely holds them.