The System Python 2.7.1 on 10.7 is also 64-bit (I checked the size of sys.maxint to confirm this). I have built matplotlib 1.1.0 on this with the standard Lion LLVM compiler (i686-apple-darwin11-llvm-gcc-4.2) and TkAgg works fine. Once you have pkg-config on your system (I use homebrew for this), matplotlib can be built without any further ado - no compiler bypasses, no files to edit. It can even be easy_installed directly from PyPI.
Just thinking out loud - would it make sense to base the dmg installer on System Python instead? My feeling is that the average user is best served in this way. There is very little difference between System Python 2.7.1 and Python.org Python 2.7.2, except that the former does not have compilation issues. Also, the System NumPy 1.5.1 is more than adequate for the average user and does not need to be replaced too. In this case, the average user can literally download the dmg and install it on a vanilla Lion system without any other dependencies. To me, this would represent the best default packaging of matplotlib on the Mac, and I would consider anything else a custom installation.
I’ve been using matplotlib and friends for nearly four years now on System Python (since Leopard) as a non-average user :-), and I’ve never felt the need to use a different Python. It certainly simplifies installation…