I love the idea of visualizing a warm Jacuzzi or beach to increase the blood flow!!
I might suggest utilizing all three sensations visual, kinesthetic and even auditory to get the most you can going when blood flow becomes a pretty serious issue. I personally like even showing pictures from a medical book (you could probably download from internet from Gray's Anatomy). I actually got pretty vivid pulsation on my skin surface when I used the idea of blood pushing through my arteries on myself .I would have him see the bright red oxygenated blood pulsing through to even the capillaries and into the very cells themselves. Hear the blood rushing through. Swish Swish Swish. Feel the pulsation as the cells suck in all the oxygen and feed the cells. Even the nerve cells are taking in all the oxygen they need and all the byproducts and toxins are being pushed into the venous system. See the darkened blood leaving the cells containing all the toxins.
I would, however, caution using a hot oil massage in reality, Diabetics, especially ones in the serious conditions, do not respond as normal people to hot oil. A regular massage with maybe lanolin or almond or sesame oil sounds like a great idea to get the circulation going. You would want to do this frequently throughout the day. Also, perhaps consider a wound care specialist nurse (you could hire one privately) to come and do some preventative work. They really know all about severe diabetics. Watch out for his sugar levels closely as this influences healing more than you know. If he is uncontrolled sugar wise, you must get a handle on that.
In hypnosis, you would want to talk about the balance that is needed but please don't let your patient ignore their actual blood sugars level in reality
. Can't emphasize that enough!