The only way I can see to do it on a device label is to include the entire oid. That means you will have to manually add every neighbor to the appearance. i.e. CDP: [oid("184.108.40.206.220.127.116.11.18.104.22.168.1.6.10101.197")]
I tried something like CDP: [oid("22.214.171.124.126.96.36.199.188.8.131.52.1.6.[Interface.Index]")] but since the interface.index is only in context on interfaces it doesn't work on the device appearance. Also the CDP neighbor is not actually part of the interface so I could not not get it to work like description below...
I put the following in the tooltip for interfaces and it works fine.
Since the CDP neighbor is loosely based on Interface.Index I thought maybe "CDP: [oid("184.108.40.206.220.127.116.11.18.104.22.168.1.6.[Interface.Index]")]" placed on the interface should show the neighbor of the interface. But it doesn't work, I suspect it is out of context.
Maybe do some testing otherwise it is going to be a big manual process...
I just use the Description on link tooltip myself.