Early renewal of Driving Licence

I have type 2 Diabetes but was put onto Insulin in May 2012. I duly filled out the DBA1 form and received my replacement licence which expires in May 2015.
I believe this means I will probably receive the renewal details around Feb/March 2015.
I have 2 questions
1/ What is the renewal procedure? Is it fill in another DBA1 or just confirm no changes since the form was filled in?
2/ Has anyone had experience or know if it is possible to get licence renewed early?
I will be retiring around the end of the year and will be out of the UK for about 6 months from Jan 2015 which means I will not be in UK to receive renewal details and will not return until after my licence has expired.
Tried ringing DVLA Medical Help Line number and just got the "We are very busy please go away - Goodbye" message

I hope they renew it for at least 3 years as the current one was for 3 years and I have never had a serious hypo requiring outside assistance, I always test before driving, and am aware if my levels are getting down around 4 and test to make sure.
After multiple calls getting the "We are busy - Go away and don't bother us" message, I finally got through and the nice lady first of all said you can't renew early, but when I said I would be away when the renewal forms were due and when the current licence expires, she said I could renew early and would send me the forms. I just need to include a covering letter stating my reasons for early application.
Stage 1 complete, hopefully the next stage will go without hitch.

Update
Forms received and sent off with letter 27Sep. New (3 year) Licence received today
If I had known they could return so quickly I could have waited at least 1 more month