Battleline Industries has released several versions of the SAPR or "Stock Attachment Precision Rifle" One for Magpul Stocks, and most recently for SOPMOD Gen II Stocks.

From the Battleline Industries Site:

"Weighing in at just 12 oz, the S.A.P.R. balances the weight of the rifle and gives the operator the flexibility to adjust their rifle stock to enhance their marksmanship skill set and personal fit for delivering precision rifle fire from an M4 carbine or other weapons platform that utilizes an AR-15 style carbine stock/buffer tube adapter. The S.A.P.R. cheek piece elevates vertically for proper eye height and relief when using scoped optics and has an adjustable shoulder pad section that moves vertically and rotates 360 degrees for optimal positioning and comfort.

A key feature of the S.A.P.R. is the rotaing cheek piece which rotates left or right 90 degrees allowing the shooter to transition from their primary optic to Back Up Iron Sights (BUIS) or a 45 degree off set Mini Red Dot Sight (MRDS) without any further adjustment to the cheek piece height."

Thanks again to Stickman for the photos:

First you'll need your own LMT or B5 Systems SOPMOD Gen II Stock and of course a Battleline SAPR.

You will then have to remove the rear buttpad of the SOPMOD stock. You'll need to keep this for later however.

You will also need the 3 Main SAPR parts,(From right to left) 1. Mounting Plate, 2. Sub Assembly and 3. Adjustable buttplate. These are easily taken apart by several screws.

The mounting plate is attached to the SOPMOD Stock. Insert the Mounting plate into the square hole at the top of the stock.

Install both anchor blocks from the front of the stock, and secure with 4 short screws from the rear.

Slide the Sub-assembly down from the top of the mounting plate until it is flush with the top of the stock.

Once flush, install the long screw through the Sub-assembly from right to left as the front of the stock is facing away from you.

Once finger tight, adjust cheek rest to desired height and apply one half turn with the allen wrench.

Loosen the adjustable buttplate screw one half turn to allow movement. Adjust elevation and rotation of the buttplate to desired fit. Once positioned, apply one half turn to lock into place.

Install SOPMOD Factory Buttpad by placing locking key block into adjustable buttplate. Push upward and lock into place.

Now you are done and ready to use your new SAPR.