Essentially you would be breaking your juice fast with vodka and would then technically be on a "juice and vodka fast". I have to say that this doesn't resonate very well with me and peer pressure really should not be allowed to dictate how you choose to break your fast.
Congratulations on your 12 days of Water Fasting and on your excellent plan to juice for 5 days to follow. I hope you will re-think what you will do after that :).