If your bg's are rising with stress this indicates not Addisons, as with Addisons stress lowers the blood glucose and your blood presure (drops when standing from sitting) and alot of Addisons suffers crave salt nearing a crisis point, for the diabetic showing signs of addisons, the hypo is very hard to treat, requiring an very hefty amount of carbs, as it's the lack of cortisol that causes the hypo and not lack of carbs...
As iHrs says, the pre-mixed regime is fine for certain people, who are happy to continue to supply carbs at regular interviews during the day, and lead a lifestyle that changes very little from day to day.. But for most people this isn't flexible enough to cope with most people who lead a very changeable active lifestyle...
Have you spoken to your diabetic team about this test and what they are asking of you, as no insulin puts you in danger of DKA, as I wondering if the hospital sort of things that you are already on MDI, so in theory you only missing the quick with breakfast insulin, and you will have background insulin in the body, to safe guard against DKA..
Edit additional info
I've asked my friend Paul to check my reply, (speaking to him on MSN) to ensure I've got it correct, he's has asked me to say, Speak to your diabetic consultant directly concerning this test.. To sort and resolve everything as he will have the knowledge, and can if necessary contact the doctor who's going to carry out the test etc..