This system works by glueing 3d printed "bases" onto and into your shield. Heat set Inserts and screws (M6!) allow to mount a grip of your own Design or choice to the shield or ditch the system alltogether.

I originally designed it to work with Shields made from EPP, which have a center cutout. although if you don't have a center cutout, you can make a different Grip and still use it with the same Bases.
You mount the Bases, then affix one of my Grip designs or your own and off you go

Concerning your Center Cutout
This is important! I made my Center Cutout 160mm in Diameter. My Grips fit this Distance. If you have a differently sized Center Cutout the Grips won't fit and neither will the "Platzierschablone". If you still like the system feel free to comment on this or send me a message and i can make a version that fits you.
You can also do it yourself, by following the steps in the Section "Custom Cutout".

Printing Materials
For the Grip PLA works, but because there can be strong Impact forces on the bases, while they are out in the heat, i wanted to make sure and printed them out of ABS.

Concerning Glue
I used Boldt Turbocoll which works really well, unless you store the shield in a boiling hot car for 2 months, which softens the glue. In a later Version i also used DeluPur, which is stronger and more heat resistant. 

BOM

• 2x Base for your Shield

• 1x Grip of your Choice

• 4x M6 Heat Set Inserts, longer is better

• print or Lasercut the "Platzierschablone"

• Powerful Glue that adheres to your Shield's Material

• 4x M6 Screws that fit your Grip

Steps

1. Put your Inserts into the holes of the Bases

2. Use a fitting "Platzierschablone" or Grip and mount your bases to it, as if it was the Grip

3. Place the Grip+Base-Combo over the Cutout and adjust it till you like it

4. Mark the outlines of your Bases' protrusions on the Shield

5. Use a Knife to carve out the marked Areas so your Bases' protrusions can slot into the hole

6. Test if the Bases fit

7. Cover the Area around the Bases

8. Apply the Glue of your Choice according to it's Instructions

9. (Presumably letting the Glue dry according to it's Instructions)

10. Unscrew the "Platzierschablone" und screw the Grip to the Bases

11. DONE!

Custom Cutout
Kudos to you! You can use the PDF-File "Griff Designzeichnung" to make your own Grip which you can also use as a "Platzierschablone". A Grip is just the Hole measurements (25mm hole center to center and 15mm center of hole to Center Cutout) and the Center Cutout. In my Case the Center Cutout is 160, but you can use pretty much any diameter you choose.
If you want or need help with this feel free to comment.