Sure! Here are the completed sentences to convey the same meaning as the originals:

1. I have worked as a volunteer for three years. **I started three years ago.**
2. She has been a member of the Peace Corps for two years. **She became a member two years ago.**
3. The last time he donated blood was ten years ago. **It has been ten years since he last donated blood.**
4. He started to work for this non-profit organization five years ago. **He has worked for this non-profit organization for five years.**
5. He has never had such an interesting experience. **This is the most interesting experience he has ever had.**