Unfortunately not.. I have a boost and sprint account I have an epic on boost and I have me s3 on Sprint... I haven't really tried yet but might give it a try this weekend, I know it reads with dfs and workshop just haven't tried anything yet, but this is one bad a** phone!
I'm also interested in the method. I'm assuming the same method to Boost will also work to move the Sprint Galaxy SIII to a Sprint legacy plan like SERO. What I've found out so far:
1) QPST v2.7 Build 366 doesn't work on the Sprint GS3 except to add the diag comm port so that QXDM can see the port. You will not be able to use QPST to manipulate Profile 0 and Profile 1 to enable 3G.
2) QXDM v3.11.36 can be used for the repair. This will get you voice, SMS, 1xRTT data working.
3) To fix Profile 0 and Profile 1 to enable 3G, CDMA Tools DFS v4.0.0.3 looks to be very promising. Don't know what fields to fill out though.
I've seen ads in craigslist selling flashing services for the Galaxy S3 for use w/ Boost, so someone has already figured this out. Hopefully it won't be long before someone documents all the steps.