this is the one i use to avoid chalice not being active at the time of meta activation:
#showtooltip Metamorphosis
/use [mod:alt] 13
/use [nomodifier:alt] Volcanic Potion
/cast [nomodifier:alt] Metamorphosis
/cast [nomodifier:alt] Demon Soul
/cast [nomodifier:alt] Immolation Aura
i activate it first with the ALT modifier, activating only chalice. immedietly afterwards i release ALT and click twice more rapidly for the rest. the quarter-second lost is easily acceptable for ensuring chalice is up at the moment of meta activation. there is not much point in activating chalice at any other time than right before Meta, since Meta DOES snapshot. it basically means you will get an extra 19% spell dmg increase for the the whole 36 seconds of Meta, with the extra 1700 mastery. popping it at other times will only get you 19% demon dmg increase for 20 seconds