SVN->GIT conversion question: how to make git svn not rebase some git commits

I am porting a medium size (2GB) subversion repository to git. I have already done an initial git svn fetch with generous filters, to filter out directories for which I do not want history. 

However, I would like to import a snapshot of the filtered directories and, here is the tricky part for me, continue using svn fetch without rebasing the snapshot commit. I would like the history to look like:

S1 -> S2 -> G1 -> S3

Where Sx is a Subversion commit and G1 contains the snapshot. 

I want to maintain this strange history so that I can gradually introduce git as a read only repository in parts of my environment, and then do a full switch over. 

Robert