Japanese voice actor is Unshō Ishizuka (石塚運昇) best known for his roles as the Narrator and Professor Okido in the Japanese version of the anime has updated his blog. He has indicated that he will appear in the anime as Pluto and that DP109 and DP110 are scheduled to air as a one hour special in January.
Unshō Ishizuka is currently learning English and his blog post is a mixture of English and Japanese which makes it difficult to completely understand. Below is a translation of his blog post:
"I will appear in Pocket Monsters as Pluto. That, however, is a 1-hour special! Galaxy Gang is up to no good again. I believe DP109 and DP110 are the episodes, and one of the episodes Riolu (Rioru) appears. After reading the manuscript of the 1st and 2nd episodes of the 2009 broadcast, I cannot wait to do the episode tomorrow. I haven't done a casting call in quite a while."
Source:
http://unshoishizuka.blog124.fc2.com/