S&T would be an option if Ray's market value is over $5 million because Ray is the kind of guy who has value mostly for a contender. In general, contending teams are at or around the cap, and thus are limited by the $5 million (or, in the case of tax-paying teams, $3 million) midlevel exception. So a team may need to spend more than its midlevel space to get him. This is how we got Bass. Orlando wanted Davis, but was limited to the midlevel. So they traded Bass, whom Davis would replace anyway, and got Davis for Bass's salary times 1.5 - $6.4 mil - which is more than they could have offered in free agency. Plus they avoid having to pay two guys more than $10 million for the same backup role, another benefit of bringing in a guy by sign and trade rather than free agency. The team preserves their midlevel exception and doesn't have to increase their salary by as much as signing a guy outright.
That's why it might work for another team to trade for a resigned Ray, particularly if Ray gets a couple of $4-5 million offers and a tax team like Miami wants to go for him but is limited to $3. Or, even if a team has $5 mil to spend, they may want to swap out some of their current salary so they retain the MLE and keep more of a buffer against going into the luxury tax territory. The new tax provisions are no joke. Teams do not want to be paying the new tax, especially as "repeat offenders" (taxpayers 4 out of the 5 preceding years - those teams pay 1.5 or 2 times the tax of other teams).
Miami, for example, would love to trade some of their spare parts and replace them with Allen (though I don't want those pieces). The Clippers may want to get Ray instead of some of their current options - Randy Foye and Nick Young, free agents for whom the Clips hold Bird rights - but may also want to preserve their midlevel to get an actual backup big man. So they might be okay with a deal like Bledsoe and Gomes ($5.7 combined next year) for Ray, bringing Chauncey back for low salary, keeping Foye and then having the MLE and a potential Young sign and trade to get a big man. (I think LA would prefer to just keep Young and Foye and have the Gomes-Bledsoe package available for a big man in a trade.)
The Spurs may be in the same boat, having the place for a guy like Ray but needing their MLE to go after size. I'm sure the Knicks would like Ray, but they have to use their MLE to keep Lin. And the Grizz are within about $9 mil of the tax level, which would be tough for them given their market, and they have to make decisions on restricted free agents Mayo, Speights and Arthur. So if they were to bring in Ray, they'd likely be letting Mayo walk anyway, so there could be an opportunity for a swap.
And if the Bulls are the most likely, it may be worth their while to sign and trade. They already will likely have to cut 1 or 2 of Watson ($3.2 mil unguaranteed), Brewer ($4.37 mil unguaranteed) or Korver ($5 mil with $500K guaranteed) to get Ray. What they'd really want to do is try to trade Hamilton ($5 mil next year, $5 mil in 2013-14 but only $1 mil guaranteed) plus a pick for Ray since that's the role Ray would be taking.