Macro's and the GCD

[pipelayar 0]

Hello,

I play on 200 ping and so doing basic shit sucks and is sometimes super inefficient. I play a warlock and would like to make a macro that pops both a major mana potion and a demonic rune with 1 button press. I know in later expansions this is possible with 1 button 1 macro 

eg 

/use x
/use y 

however in vanilla when i make a macro like this it only uses 1 of the items despite both being off the gcd. This is frustrating because again i have 200 ping so I feel like i have to wait that much longer to start slinging shadowbolts and I want to maximize uptime, (even if its 1/5th of a second)

Am I fucked because vanilla sucks? Or is there some crazy macro that can do what im asking?

[WobLight 5]

try adding /run SpellStopCasting() between the two /use