Just to echo Papadroid, just because Sprint and Verizon use CDMA, does't mean you can flash. You would need the RIL's for Sprint's 3G network (which in my opinion is SLOW) and then you'd have to do a lot of work to get the Thunderbolt to work.
Also, again, Sprint doesn't have LTE and even when it did, you'd have to do the same thing all over again, which is time consuming to say the least.
To wrap it up: No, its not within the realm of happening.