You'll need a lua unprotector for this, I recommend project sn0wball. What they do is compensate for the lag and allow you to use trap launcher and the specific trap in one button. Not complicated or anything but it's here for easy access and for those who don't have the know how to do it.
Code:
#showtooltip TrapNameHere
/run local _,d,_ = GetSpellCooldown("TrapNameHere") if (d == 0) then CastSpellByName("Trap Launcher") end
/in 0.35 /run if UnitBuff("player", "Trap Launcher") then CastSpellByName("TrapNameHere") end
Depending on your latency you're going to need to change "/in 0.35" to a higher number, if anyone has any better solutions please post