Very similar to the Tier One you have been looking at;
Spartan Sling Point Rail.
www.uttings.co.uk
Actual photo of the product itself;
Discover the Salamandertactical Micro Sling Point Rail, a compact Picatinny rail for versatile mounting options on your rifle stock. Perfect for accessories!
salamandertactical.com
You will need to attach it with an M5 countersunk bolt into the existing threaded insert, (where the current sling stud resides), and an extra shorter M5 countersunk bolt plus nut & washer passing through the stock and forend grip, (new hole required

).
All assuming it's a Tikka that your working on?
PS The base of the item is not perfectly flat but ever so slightly radiused however, so is the Tikka forends and forend accessory grips.