I really wouldn't worry too much.
With the net, and burning, music is pirated all over the place, and no-one is going to worry at all about your use of the music on this occasion.
If possible, in your film credits, just put something like -
Music from Elbow and Sigur Ros - all copyright restrictions apply.
This will show that you are aware of copyright, but as i say, it is extremely unlikely that anyone from the bands, or their record companies, would know, or be bothered.
If your film gets to Cannes next year, that's a different matter!