I did a little more research and was able to find this on Handango.

http://www.handango.com/PlatformProductDetail.jsp?siteId=1&osId=946&jid=A8 ABF1D93FXBC5B6X234D163EBD4AE27&N=4294917542&Ntt=ME TAmessage%20Language%20Support.%20NOW%20also%20Jap anese%20Input!!&R=187122&productId=187122

It does require a subscription, but it does do what you want.

Still researching about loading japanese on the pearl though. I thought I saw it somewhere.