OK, so it seems fair to answer this - since the question was about _selecting edge ring in UV editor_. 

The way to do this is by:

 - enabling "keep UVs and edit mode mesh selection in sync" (button in the header of UV editor)
 - just Ctrl+Alt+RMB clicking on a edge in 3D editor (it will be reflected and be perfectly editable in UV editor)

Were the question about _straightening the resulting selection_, it would seem there is no way to do this for now.

[Thanks to Mr Zak for clearing the confusion.]