I actually just forced roam on my phone without root or an app. I have the Verizon PRL profile and I just manually tell my phone to use it.. Then it uses Verizon and roams with them. When I am done and want to use Sprint's network I just go to my phone status and update the PRL and it will go back to Sprint. I simply just swap the Verizon PRL in when I want to use the roam and bam.
I would host the file here.. But.. Is it against forum rules? Don't think so but I don't want to be banned.
edit: as you can see they were funny with the PRL number lol.