How to add 2 drives to an existing RAID 5 array

I have a Dell PowerEdge R620 with a 4 disk RAID-5 Array.  Using a PERC H710 controller.  The current drives are 300GB 10k RPM SAS drives.  I would like to add 2 more identical drives to my existing array.

So far the only way I see to do this is to back up all of my existing data to an external source, add the new drives, recreate the array, and then restore the data onto the new array.

Is there a way that I can add the new drives without having to build the entire array from scratch again?

Nate