Porcelain specific metadata under .git?

So I'm reaching a point with my Eclipse plugin[*1*] where its actually doing something with a GIT repository and I want to store a ref (to a tree, not a commit) under .git/refs/eclipse-workspaces to help the plugin cache state between workbench restarts. But there doesn't really seem to be any policy to what paths under .git are available for Porcelain and what definately should be off-limits.

I already assume/know that refs/heads and refs/tags are completely off-limits as they are for user refs only.

I also think the core GIT tools already assume that anything directly under .git which is strictly a file and which is named entirely with uppercase letters (aside from "HEAD") is strictly a temporary/short-lived state type item (e.g. COMMIT_MSG) used by a Porcelain.

But is saying ".git/refs/eclipse-workspaces" is probably able to be used for this purpose safe? :-)

[*1*] The Eclipse plugin is getting close to something that is worth releasing as an early alpha for other developers. I think I finally found the last bug in the pack reading code and am now working on the basic operations (add/remove/commit/status). I hope to have all of that working within a few days, at which point I'll publish/announce a public GIT repository with the complete source code and an Eclipse update site for those brave souls who might want to just install it.