I'm currently shuttling between short term assignments through an agency.
Your PGCE is fine to teach adults (not that I'm bitter that my DTTLS only lets me teach children in FE colleges not schools).
Personally I would take a powerpoint on a memory stick and email and just use that on the IWB.
I think the key to micro teaching is to actually teach something. I like to have a handout for the interviewers to fill in, preferably something they have worked out.
One thing a lot of adults have never been shown is that the divide symbol is actually a fraction with dots replacing the numbers.
I could make a 10 min micro teach out of just that, I might also bring in sweets to be 'shared', although if I do that I do tell the students/interviewers that if Ofstead are around they will be pieces of fruit. Smarties are good as they are like counters, lidl has large tubes on offer at the moment.
So one tube of smarties divided by 3 people means they all get 1/3 but then count them up (you obviously need to do this first) and see what 1/3 of 16 is (or how ever many you have put in the tube)
You can then explain that this caters for visual, kinesthetic and auditory learners, and the handout underpins this for reader learners as in Fleming's VAK/VARK model of learning styles.
For extra brownie points take in he handouts in on coloured paper - either 4/5 different colours or all yellow with the text in bold in a sans serif font. The colours are for dyslexic students and the yellow for VI students. This is particularly relevant for adult learners who may not have had a diagnosis at school and this is why they have not got qualifications.
Good luck. It is THE most rewarding thing to see a light go on in an adults eyes when a penny drops and they 'get' what they have tried to understand at school when they were children, with their own children helping with homework and you are the one who has explained it to them.