You don't give any model number so it is difficult to comment. But have a look at http://www.hifi-remote.com/forums/dload.php?action=category&cat_id=87. There are six Custom Remotes there for Panasonic.
If yours isn't there come back to me and I will have a go at building a remote for you.
Thanks AR42. I looked at JP1 but don't see my Panasonic DMR-BS750EB blu-ray/2xFreesat. Using Sling option for a Panasonic (DVD) DMRE HS2EB gives me some basic functions such as on/off channel change and play (current) HDD file, but no menus. The DMR-BS750EB is by no means new and has just been superceded by a new model so not sure why there are no Slingbox device options for it. Maybe it's because I only have a Sling Classic, which I think is unsupported by Slingbox Beta.