I don't think Tracer plugin is suitable: too variable, especially when associated with keyframes. The only way is the second video: Roto + Motion tracking. In theory it is possible to associate a green screen with Cinelerra's Motion Tracking. But this plugin is slow, heavy and complicated. I hardly reach good results, even more so if there are curvilinear as well as linear movements. Maybe it's better to work manually with mask + keyframes (without using green screen); but the result will never be as good as Roto + Motion Tracking, because of the Edge Jitter and the gap between background and object. (in your video you can make a "de spill" to mitigate the green halo.) Roto + Motion Tracking would be a wonderful addition; DaVinci Resolve, Premiere Pro and Edius have these tools even without going through After Effects or Fusion.