Use a cutting of semi-hard wood. taken summer/fall. apply 0.3% IBA (Rooting hormone) stick in well drained soil & mist taking up to 90 days to root. The olive is not normally hardy in your area so will need much winter protection

I had the same question mainly because I bought a dwarf Olive tree online, and I have killed it! Container olives might be harder than the ones in the ground, but space demands it for me. We were golfing and most of the olive trees on the course have sprouts at their bases. I ripped a few of them off, stuck them in a cup of water and brought them home. I dipped them in rooting hormone. They are outside now (semi shade) in potting soil covered with a plastic dome (mini greenhouse). It will be a miracle if one roots, but worth a try. I did find this link with lots of information and pictures. Very informative.

Here is a link that might be useful: How to propagate Olive Trees