ive done them- but use straight cutters- and wedge from behind as normal
easiest way is set as single pass (a must with dovetail cutters- and ensuring the plunge is behind the tread- dont want a bigger circle showing)
id set up as a pocket toolpath at depth required . eg 20mm
measure your cutter diameter roughly at 20mm up from bottom with a caliper (or work out with trig if your real fussy)
use that diameter as your tool diameter.
now test the cut on a sample piece. offer up the tread and see the fit- either too tight or too loose .
adjust the toolpath allowance setting + or- to suit and re calculate.
test again- adjust as necessary and your ready to go.
might seem an odd way to do it- but thick timber can be expensive to mess up!

or start - make the pocket smaller by say 3mm. when checking fit - if say too tight by 5mm offset the vector out 2.5mm and just do an inside profile cut to that vector