So if I'm understanding this right, all you want to do is add some type of bipod - but you currently have the plastic (poly) handguards and NO railed handguards - correct?
An easy way to do this WITHOUT having to buy their kit, would be to add a rail to the bottom of your plastic handguard first - Ergo rails
Next, what kind of bipod are you thinking of adding? Do you want something like a Harris that allows you to extend the bipod for kneeling or sitting position or just for prone?
After adding the rail, you would add an adapter like this: Harris bipod rail adapter
Your bipod would then attach to the sling swivel on that adapter.
I know...kind of a long way around, but it would accomplish what you wanted.
OR...you could attach a GRIPOD to the rails. Gripod bipod assembly
This would give you a vertical front grip to hold onto, as well as a bipod when you need it, the legs retract inside the vertical grip.
OR...you can always change out the handguards and put on a rail assembly, this would allow you to attach a lot of different things, (lights, bipods, lasers, etc)
Just a couple options, I hope that helps a bit.