You change all the unit prices in gold to be hundreds of thousands of gold, you make the recruiting expedition require collecting 50,000 gold or more from your mine (which is tedious as hell to upgrade because no one really cares about assisting when they get not a thing out of it! At least boss blitz used to reward both participants!), then, you finish a recruiting expedition and your reward options to pick from are two different unit cards or, wait for it, 1,000 gold!!! Woohoo!!
Who thought this out huh?