Short answer is no.
However, I am seriously considering making a contrib to git to make subtrees write their last push/pull targets to a config file.
You could sort of do a similar hack for now by writing a git hook, which saves which repository was used, and write a wrapper command that uses the saved value.
The subtree documentation sort of boasts it's lack of config files, with the statement:
Unlike submodules, subtrees do not need any special constructions (like .gitmodule files or gitlinks) be present in your repository, and do not force end-users of your repository to do anything special or to understand how subtrees work. Reference: git-subtree.txt
I think that's great that a config is not needed to get the code setup, but at the same time, it wouldn't hurt to have one just to provide meaningful defaults for running the command with fewer arguments.
I'm currently implementing subtree support for tortoisegit, and I'm faced with the same problem. I'd like to make it so when you choose to do a subtree push or pull on a folder, it can remember where that folder was last pushed or pulled from. For now I'm having tortoisegit write to a config file, but it really should be done on the core command.See the pull request discussion here.