Crossover licks are easy to play when you look at them from another point of view. I use the right hand position to change crossover licks. The examples below will show you this easier than it can be explained with words.

The right hand picks an alternate in one position and then skips to another. The last example shows two forward rolls in position 8 and position 5. The position is where your thumb is located.

Above the forward rolls are seen in six different positions. To make a crossover lick you can do variations of the positions. It's your choice whether to play a two or three finger crossover movement. Either way will work.