We have thought long and hard about doing a "deposit bonus" but after going back and fourth with our developer we decided it is now in our best interest, since it can easily be abused.
We have also thought about doing Royal Flush and 4 of a Kind bonuses on the ring games. Would anyone else be interested in this and would it encourage you to play more on the ring games? If so we can possibly get this implemented.
Since you are trying to get some action for your ring games then it might be best if you make a promotions for "happyhour" for a rakeback of X percentage.
The promotions of getting either royal flush or 4 of a kind is rather hard to get and wont attract a lot of people for the ring games.
In fact, the deposit bonus could serve more for the ring game advertisement. You could add up a deposit bonus which you will only get if you have enough points for it from which points can be gotten by contributing some rake or get it from the GTD by paying the house fee