Unfortunately, the only access point that can handle Mesh is the 1500-series. Mesh isn't meant for indoor applications like the 1131AG is meant for. Mesh is meant for city-wide deployments and wireless coverage.
Your only option using 1131AGs is to get a cable out there somewhere. If you purchase a couple of 1242AGs in autonomous mode, you can set up a mesh-like link using link-role flexibility. You can configure your A-radio to be a bridge link, and configure the G-radio to service clients. This can only be done 1-to-1, though, so you'll need two APs for every one you need in an area without cabling. Hopefully that makes sense.
You can use Enterprise MESH which is MESH for indoor uses. It is available in the later releases of code. Enterprise MESH was designed for use in areas where cabling is an issue. It requires separate licensing. See the link below for more info.