Well I feel like if you do really havea great interest in Medicine, you should find a volunteer role/work experience that excites or interests you. No need to go round the houses to find a way to try and make your interest look greater, if your interest is enough it will show through how much you do and the enthusiasm you convey about it.
You could have 1 week worth of experience Vs someone who did 6 months of it, come interview time if you talk the talk better and explain in a logical, clear way what you learned from that experience, why it was interesting and why it means you'll be a good addition to their university. You will probably get the better of the other applicant who verbal dihorreas about everything they did not making their point appropriately.
If the work you find yourself is genuinely of interest/excitement to you, then you will learn a lot and not just be a bored errand boy and that will come across in interview. Usually quite easy to tell apart people who have a genuine interest and those who have endured something just so they can say they did it.