Originally posted by CarlJF although you can blur the background of a portrait taken with a UWA, there's no much you can do about the ugly perspective of the portrait. It will not look at all like a Brenizer made from shots covering the same angle but taken with a large apertue telephoto.
Not so; using an UWA lens doesn't create perspective distortion; standing too close to the subject does. If you were to try this out, using the same camera position each time, you'd get a similar perspective. Differences would be due to factors such as barrel distortion in the UWA, and which stitching algorithm you chose (spherical, rectilinear, other). Software stitching effectively creates a wider-angle lens from the multiple shots.
To the OP, in most situations, memory is cheap. By all means try to simulate the effect with software blur and see if you like it, but as pointed out it may not be very convincing if the in-focus subject is not well isolated.
---------- Post added 2016-01-09 at 01:14 PM ----------
Edit: Mike's technique looks good, too. One could combine the two shots using focus-stacking software, if the masking proves fussy. Either way there is the potential problem of halos around the subject, caused by the fact that the subject "spreads" in the out-of-focus image and covers some of the background. But Mike's example looks very clean. I'm going to have to give this a try.