Here is what Ive done recently to my 3-4year old juniper to develop a nice thick trunk at the base.

This is my victim. I bent the tree last year, so I thought this year is a good time to develop the base.

I went ahead an cut the trunk at the bottom in 4 equal parts with a sharp knife, and stuck 2 pieces of wire to keep the trunk quarters away from each other.

I applied then some root hormone (I only had the soft wood one, maybe the hardwood would be better) to promote root growth from the freshly sliced trunk.

Finally I potted the tree in a large pot, to allow plenty of room for root growth.
Basically the idea is that roots will start growing where the trunk was cut. In january I will check the progress of the roots and tidy them up a bit and put it back in the soil. Hopefully the roots will start fusing with each other eventually, and they will form a new base of the tree, which will later be exposed.
The tree is in the shade now for 2 weeks, I will keep it moist to allow roots to grow and absorb water since I cut most of the roots away. I will then start
feeding it and I will put it on the sun to grow.
What do you guys reckon?