Actually, Bokeh is just the result of blurring image parts with high brightness contrast using the right kind of filter kernel (f.i. disc or hex, gaussian wont work->too soft). HDR DoF is the usual application. Building larger kernels isn´t such a prob with the hex filter since it has linear complexity. Adding additional passes with the right sampling offsets can give you quite a large radius. But I´m not sure in how far this works well for the disk kernel. A common technique is to render sprites to achieve the bokeh effect where it is necessary. This way you can have quite large, arbitrarily formed results.