Step 1: Step 1: MATERIAL
I purchased two packages of Velcro from the Dollar Store, and used a stapler and scissors for the installation.
Step 2: Step 2: INSTALLATION
Flip the first two pieces on their back, observe the natural spacing between the bases. The cushions on my unit do not allow the bases to be in contact (see the photo). I opted to use 3 strips of Velcro along spots that had sturdy braces to staple them onto. Cut the lengths of Velcro to optimize the anchoring. Peel back the sticker backing on the "hook" side of the Velcro and staple it onto the the frame. Cut and trim the excess hook Velcro: the loop side will be doing all the work.
Now flip the third piece on its back and the turn the middle piece so that their relative position is respected. Repeat the steps described above. I elected to leave the sticker backing on the loop side of the Velcro; the dust bunnies don't need any help finding a home.
Step 3: Step 3: TESTING
Start by joining two of the pieces and installing the loop Velcro on the other end of the middle piece of the sectional. Now, carefully flip it back into place, a second set of hands is useful for this step. Carefully place the third piece onto the Velcro that should already be sticking out from under the middle piece.
Test it out and enjoy.