Yes you can, I do and have done for a while now ...dosn't half save money!
I would say the key is the how the oil is prepared (used oil) but new oil can go straight in. For best results I have an oil heater fited that runs off the radiator, but you can mix your oil and diesel in a percentage dependent on the temperature of the weather without a heater.
get a copy of the DVD and it'll tell you a lot.
Birty1