On my R1150R I bolted a couple of black flat pack connector blocks to the pannier.
This simple method has held fast for the last 20,000 miles.
Not very pretty but it works.
Another solution I have seen uses a spare left hand side footrest bracket inverted and fitted on the inner side of the subframe, but I think this involves some cutting and grinding of the footrest bracket. By using longer bolts with nuts and some spacers you can keep the original footrest in place.
Hank.