Since the refactoring I did in 2.4 for devtool/recipetool fetching new source, we actually need to create a "dummy" recipe in order to be able to run do_fetch/do_unpack/do_patch with the desired SRC_URI, then run the tasks, then delete the recipe. To do this we look through BBFILES and pick a place to put the recipe, favouring the workspace layer if it's present - but it may not be if the user is running recipetool and devtool has never been run. 

This current method is a kludge. We could really use a place to put these dummy recipes temporarily without potentially writing things into a random layer in the user's configuration. Of course we could add a layer on the fly, but that would trigger a full reparse of the metadata which I think would be worse.