selecting and cloning

At this moment I am working on pictures of paintings. These paintings are white, photographed on a white wall, so there is a little, but hardly any contrast between the painting and the wall. Making a general selection and fine-tune it with the luma-range tool doesn't work, neither selecting the painting with a brush tool. In this case a lasso-selection tool, like the one in Photoshop would be very helpful.

An other request is for the clone tool: if you could - like in Photoshop - make a selection on forehand, before you start to paint in the clone. So that I can decide where the clone tool takes the pixels instead of like it is now that I have to correct very often a clone that Capture has decided for me.