I know I have done it the other way around. Diesel has more lubricant in it, I used to dump our Jeta in the GSE after sumping tanks to check for water. The owner of a company I worked for went out and purchased a 500 gallon tank, he would take advantage of every time we had to do tank work and had to sump the tanks dry below the level the pumps would quit at. We would dump in a couple quarts of motor oil.
Sir Branson I understand has run a Bio Diesel test flight in a 747. It was well publicised , I am sure the details are within the realm of Google.