1) Buy a Boss. Whoever would go first has the option to pay 10G and go through the deck to grab the person they want for Boss. Each player then has the choice to do so in turn. You only get one shot - bid or pass.
2) Buy a Racket. Same as 1) but with a single Racket of your choice.
Bear in mind that if you use both of these options, come bidding time you will have people potentially ranging from 10Gs to 25Gs (or 30Gs for the Vegas Bunch). This will change the bidding and add a bit of uncertainty.
There's one more option you can use for smaller games: choice of Mob. With 4 or fewer players, deal out two Mob cards to each player; each player has their choice of which mob they take.