Usually we think of layer as being right round the trunk but a similar technique can be used in smaller portions of the trunk. As
@leatherback mentioned some cut out a series of small windows where roots are needed. I have cut a strip of bark out between 2 roots where I wanted new roots. I have also drilled holes through the bark where roots are needed. Small holes like that normally heal up too quick for roots so a matchstick or toothpick dipped in root hormone is inserted into the holes to prevent that and help induce roots better.
I am about to ground layer one as the roots it has are just coming from one side, but if there are other methods I might try them first. Thanks!
In this case I would try the part layer so cut a strip of bark round the side you need the roots. Make the top of the cut level with the roots you already have on the other side. Bottom of the cut will be around 1 cm below if possible. Strip out the bark and scrape the cambium off the wood below then brush on some root hormone. Root prune all existing roots quite hard then plant it a bit deeper in the pot so the cut is far enough below soil level so it will not dry out. I often add sphagnum moss close around the cut as I have heard it has special properties for rooting but not sure if that is necessary. Just make sure the soil does not dry out while the cut produces callus and new roots (hopefully)
If cutting an entire strip out worries you you could try the drill and matchstick method as it is less invasive.
I have found that the stronger existing roots usually need to be cut hard a few times over coming years to force the tree to grow the new roots to equal size.
Good luck with the tree.