Make the skills based on Tornado (dummy skills here) would make it channel, Here comes trigger:
When you begin cast spell create dummy unit at your position that cast tornado at same point with you cast. Set dummy=lastcreatedunit
Give trigger if caster ordered with unit, with point or without point (This use 3 trigger events, so anything you command to caster 'stop' or 'hold position' it will check if you stop channeling)
Then wait 5 seconds and kill dummy