multi stage spells?

I was wondering if it was possible to have multi stage spells using the turnoff function (as in immolation) and triggers.

For example when someone uses a spell the hero "channels". The user can turn off the spell and triggers can probably cause another spell to be cast. the spell can vary depending on how long the hero "channels".

The longer he channels the more stages he stages he goes up untill a max stage. When he turns off the spell, depending on what stage he is on another spell will be cast.

I'm not sure if this is possible. Any help will be appreciated.