You could help with the bumblefoot to a degree, but inactivity is part of what has caused it, so there is only so much you can do. In any case, bumblefoot is notoriously difficult to cure, but it can often be managed very well.
Bepanthen will be of use again - hopefully you have kept hold of the tube you had for the sores on his legs a while back!
If you have a shallow dish big enough to sit Boris on, you can fill in with a little bit of saline/salt water, just deep enough to soak his feet for a couple of minutes, then dry them well and apply the Bepanthen. Aim to do this twice a day at least.
Whether it is bumblefoot or a similar problem, if the feet are swollen and have sores or redness on, this routine should at least soothe them and keep them clean. Is it his front or back feet/hocks that are sore?
If you are able to put an order in to Gorgeous Guineas (
www.gorgeousguineas.com), they do two creams that could help a lot. Happy Soles is formulated for bumblefoot, and Perfect Paws is ideal for pretty much any foot problems. GG do ship to Australia, it usually takes about a week though. I have used both Bepanthen and both the GG products, and in terms of foot troubles, I do prefer the GG stuff. Bepanthen will be just fine if it is all you have got/can get.