Insert a /click in the macro.

Create an assist macro and put it in say the first button.

the first button ID is ActionButton1 "i think"

than create another macro for your attack.

#showtooltip Frostbolt
/click ActionButton1
/cast Frostbolt

something like that I am not in front of my macro's so I am doing it from memory

do a search for some of my post I know I mention /click assist somewhere. This is not my idea I gleaned it from the wiki somewhere.