Would be better to find some other way to handle git (maybe calling it version 0.0.0+git20140917 or similar, or press upstream to release a snapshot with a sort of release number)
I agree with you. In those cases I usually do 0.0.git20140917 , but anything along those lines would work.
If you already know the number of the next release, whenever that will happen in the future (say, for example, they are preparing release 2.4 but it won't be released for a while and you prefer to get it from git), I tend to use 2.4~git20140917
If a previous release has already been published (say 2.3), but you prefer to get the code from git as it is substantially better, you can use 2.3+git20140917