I don't think this will be strong enough to support your iPhone 5 in the dock. That Adapter is more for third party devices with hard wired 30 pin cables, like some older car stereos.
I don't think we have seen a solution for any type of Dock or Dock adapter.
Same type of thing for speaker docks. The adapters don't seem to support analog audio out (iPod out), so even if the adapter would hold your phone in place, it won't pass audio unless your dock uses the "mass storage" interface and takes over control of your iPhone...
Maybe some of the more expensive speaker docks do that, but the cheaper ones (like clock radios) do not, and I don't think any of the adapters we have seen will work for those.
I think the solution is an adapter which contains a 3.5mm headphone plus in the adapter in order to pickup the audio. The only think I have seen like that is a mock up in this italian blog:
Agreed about the analog audio, but as for the dock controls too, well yeah they are probably the same setup - iPod Out, so maybe that wont work eithor. I guess I'll try next friday and see