I made several hundred 2" clumps inexpensively in one day using this process:
1) Purchased some boxes of the thinnest 2" washers I could find. I think they were $17 USD/100.
2) Bought a length of appropriately colored rope/twine.
Unraveled the rope strands, then cut into the desired length. I bought quite a bit for under $10. USD
3) Soaked the rope lengths in hot water to straighten them out, then let them dry.
4) Mix up a batch of Durham's Water Putty and add some cheap craft paint to get it to whatever color your base terrain is. You don't need to do this step as you can paint the bases after everything is dry instead. I did it as it saved me time from painting the bases after and, if for some reason this chips or a chunk of the grass comes off, the base coat is still there.
5) Coat the base of the washer with Durham's Water Putty. The nice thing about Durhams is you mix it on the fly and control the consistency. Keep it a little thicker. Work in small batches because it can dry hard in 10 minutes.
6) Grab a small handful of the rope, line up the ends, and stick it in the Durham's. The whole mess will be thick enough to hold itself up.
7) Let it dry overnight.
8) Go back and paint the edges of the washer. You can now terrain around the bush clump as desired. On the majority of my washers I was able to almost entirely load up the whole surface with my tall grass, so not much space left to add terrain. I wanted a full 2" washer to get that effect that the OP is looking for.
Now with a few hundred of these washers completed I can cover several square feet of table with solid grass. Being on 2" washers movement in them is easily done by removing washers and putting the troops in their place.
I've received a lot of compliments on these and several people have asked to buy them from me. I'd post a pic but
TMP technology and pictures befuddle me.
