A few points in no particular order.
1. Air Ambo generally have ZERO training hours; all flying is on task. They will be able to do winching...... If EASA allow it and the charity pay for suitable training. It's not impossible!
2. Paramedics are not crew, they are pax. If you only winch them down, it's winching! If you only use the winch to reposition, it's winching. The clue is in the name. If you use a winch, it's feckin winching. See 1. for reasons to do it.
3. The met police spent a fortune on winching equipment for 145, they might sell you it cheap...... and unused, not through choice. Hint hint
4. YAA have some excellent pilots and crews, some with SAR experience, they would cope
5. It would be expensive, but it would be a really useful capability, especially when your nearest SAR unit is sooooooo far away