Need help triggering - Can gold be converted into the mana of a unit?

[dontsnoozeondalose]

Let's say you have 500 gold

and you have a building has 0/1000 mana

But a trigger somehow gives the building 500/1000 mana

I've been trying hard to find a way to trigger this. But it appears that the set gold function is unavailable

So is making this trigger impossible?

 

[Maker]

Player - Set Player 1 (Red) Current gold to ((Player 1 (Red) Current gold) - 500)

Player property.