I have used Aquaphor to incorporate epsom salts into an ointment base. It is tricky. One has to dissolve the epsom salts in a small amount of water first (use the least amount of water possible). Measuring the salts without a pharmaceutical balance is also very difficult. It was messy and I didn't get a huge response when I did it.

There is a cream available from Kirkman labs. It targets autistic children, but anyone can use it:
http://www.kirkmanlabs.com/ViewProdu...roup_ID@1.aspx

I have this link on my magnesium thread, but I put it up here again. I think it is quite expensive for a small amount. But...
for kids, it is the safest way to deliver magnesium to them without risk of toxicity etc. It has a fixed concentration also, which makes it dependable.

Looking at the magnesium "oil" I see it is just like a liquid form of epsom salts. Using the Swanson product is much more affordable, but it does not contain a transdermal facilitating base like the medications we make and see for pain relief...special formulas to carry the active ingredient into the deeper layers of the skin and into the blood stream.
The skin is a fatty acid layer, which repells water...and this is an aqueous solution basically (the magnesium oil), and hence limited in absorption. The epsom salts penetrate locally as well, but I don't really think they get into the major blood stream where they can be transported around the body.

On my magnesium thread that Rrae put up kindly here, is a recipe for making a fatty acid containing product using milk or magnesia and a coconut base.
Here is the beginning of the recipe:
http://neurotalk.psychcentral.com/post608661-182.html
There is a discussion following that post, where I try to clarify a few minor points about the content of the coconut oil...etc. Those are minor compared to the recipe shared. If you were going to try to make a real cream, this might be worth trying.
The oils in the coconut would help move the magnesium deeper into the tissues. A real transdermal vehicle would be best tho.