the question is why would you want to in the first place, the price you would pay the converter is not cheap (in my books) which means a further cash injection woudl give you a whole new lens.
you get with a 1.4 tc (£200 ish)
119mm @ roughly f/2.5
a canon 100mm f/2 is around £250 upwards
or Canon 135mm f/2 L £600+
granted the L lens is dear compared to the converter but the quality of the 100f/2 is better than the converter and the 85 1.8.