I'm sorry to say I don't have an answer for what you're trying to do, however, if I may, I'd suggest you use bump/normal maps or even displacement maps in-place of individual tiles. It should lower render times and overall poly-count.

I have yet to experiment with "Transfer maps" but it seems like something you can use if you do decide to make the switch.

Here is a basic tutorial/look into what it is and what it can do.

Creating Normal Maps -Baking using Transfer Maps in Maya - YouTube

Just create a big enough rectangle to cover all of your current side-walk, go through the "Transfer maps" process with normal or displacement maps, and apply one basic texture to that single rectangle/geometry.