Around here we`d pop in what we call a triplex breaker it has DP 30 and either 2 20a breakers or DP 30 and 2 15a breakers built in a small package.Take the 30 DP hot water heater breaker out and either 2 20a breakers or 2 15 amp breakers out and this device will free up 2 spaces.All the home centers have them as well as supply houses.
Hope this helps,They are manufactured for several different panels Saves Time and money.
