Nobody has bitten, so I'll throw some explanations half formed ideas in, incase they are of use. I have no knowedge of how well your T5135s might play with Windows 2012 and only very limited knowledge of a previous version of CRM.
You don't say if the Windows 2012 server is ready doing anything else, for example if it is the CRM server or a spare box that you can be more flexible with.
For a RDP clients, you need to run a remote desktop session host. This would create an operating system instance for each connected user. Were you to do this, then thin client user would end up in a sesssion resembling a Windows 8 desktop. From there that could connect to CRM in the normal manner. Note that this is not a zero cost option, as you would need RDP CALs (and Windows server CALs) for each user or connecting device, in additon for the relevant CRM licences.
Making a server an RDP session host means that you don't want that server instance to be doing do anything else. RDP session hosts should really perform only that role.
If the server is already doing something else but has some spare capacity (CPU, DISK, and Memory), you could install the Hyper-V role. This would allow the server to run a second instance of WIndows 2012 as a virtual machine, dedicated to being the session host. The windows 2012 licence allows you to run a second server in this way. The thin client would attach to the session host, and launch CRM from the desktop that they end up in.