Here are 4 trades that would bring in a SF who's better than Gee without giving up a piece of the core:
1: Jarrett Jack to Denver for Jordan Hamilton and Randy Foye
This makes a lot of sense for Denver since Hamilton will be scrounging for minutes anyway when Gallo comes back. Meanwhile Randy Foye has been garbage for them at SG (9 ppg on 36% shooting) and Jack would be a big upgrade.
Jordan Hamilton is no star, but he's shooting a consistent 37% from 3 over his 3-year career, and he's pretty solid defensively as well. If he continues to develop (he just turned 23 in October) he could be a high-quality 3&D roleplayer for years to come. Randy Foye is obviously not very good and is just coming over for salary reasons. We would need to make sure Mike Brown understands that he is not supposed to be part of the rotation.
2. Tyler Zeller and CJ Miles to Dallas for Jae Crowder and Wayne Ellington
Dallas has resorted to such bizarre moves as starting DeJuan Blair at center, so the addition of Zeller would give them some much-needed depth there. Miles could seamlessly slide in and take the 15-20 minutes Crowder's been playing off the bench, and Wayne Ellington would not be missed at all (he's not in the rotation at the moment).
Most of Crowder's value comes on defense where he's shown potential to be great, but he's also improved on offense since his rookie year, shooting 40% from 3 before going cold in December. Ellington would be extra depth in the backcourt, and could scrape out a rotation role if he finds his shot again.
3. Jarrett Jack to Charlotte for MKG
I've brought up this trade before and I still think it would make a lot of sense. Off the bench Charlotte has Sessions (40% from the field, 22% from 3) and Gordon (36% from the field, 22% from 3) in the backcourt, both of whom are atrocious defenders, so Jack would be a huge upgrade. MKG has been out for three weeks with a broken hand and Charlotte has been much better without him (6-4 without him, 7-11 with him). They're apparently open to trading him too after a disappointing start to his sophomore season.
This trade is much more of a long-term play for Cleveland. MKG wouldn't be much of an upgrade short-term over Gee, but at 20 years old he still has a lot of potential.
4. Earl Clark to Cleveland for CJ Miles
Cleveland could use extra depth at PF with rookie Anthony Bennett not performing as expected, and...oh wait, we already have CJ Miles. He should probably be starting at SF.