so i want to add a perk that reduces spell charge time for the destruction tree.

however, spell charge time isn't in the list of modifiable attributes.

can anyone think of a workaround?

You would have to do some scripting and SKSE would be required. SKSE MagicEffect functions allow you to modify charge time. You could make the perk add a new scripted ability that modifies charge times of spells that the player knows. It also might be a little tricky to handle custom spells added by other mods.