The NO HOLD CONFERENCE feature is available in four flavors. If you have the NTPs at hand look in the Software Features Guide under the same title. You might try the Conference-Autodial(CA) version and put the RNP feature code as the ADL digits for the key. You will have to test this out! I have not tried this. This is just a wild guess that it might work. Or wait and see if anyone else has another idea.
KEY xx CA 4-(16)-23 y....y Combined NHC and Autodial key, where: xx=key number, and y....y= target number stored in the key(max 23 digits).
Hope this helps!