A possible solution:
You could give a hidden ability based on Channel to all of your units. Then whenever you order a unit to right click/attack a Destructible replace that order with the Channel ability order. It will look like your unit is running up to attack the destructible when in reality it's running up to begin channeling our hidden ability.
Then make sure to set the cast range of the Channel ability to be equal to the ordered unit's attack range (you can do this with with triggers). And instead of playing the Spell Channel animation the channeling unit should play it's Attack animation. Then have a timer trigger that periodically adds gold to the owner of the channeling unit while also damaging the destructible (set it's life to be equal to life - casters damage). You can calculate the caster's attack damage with triggers too.