other than documenting the wwns of the source and target LUNs and matching these to VM on the DR site, I couldn't come up with any solution. Another tip is to create a small txt file on each RDM from the OS level of the VM and note the name of the VM, drive letter and other properties you want to know when you need to manually attach RDMs to VMs. If you then accidently attach tje wrong RDM to a VM, at least you can see which VM that RDM actually does belong to.
Or buy a product like SRM (Site Recovery Manager). I'm not sure if that does all this for you, but if it does, it sure saves you from a headache in case you have many many VMs with oh so many RDMs.