As you have found, kindlefix only works with OverDrive Secure MOBIs and BoB sells both OverDrive and MobiPocket Secure MOBIs.
You should be able to completely strip the DRM using mobidedrm, which is a Python script that is used similarly to kindlefix (but with an additional argument). Also, use your PC's PID (it typically contains a $).
Obviously, since mobidedrm strips DRM it has a different legal status than kindlefix. However, doing this for personal use on ebooks you bought harms no one.
The best place to start to look for copies of the MobiDeDRM python script is in the responses to
DarkReverser's Weblog. Since 0.05 just came out, start with the most recent responses. The Dark Reverser originally posted the python script (source code) to pastebin.com, it gets deleted from there periodically but if you find it there the download is .txt which needs to be renamed .py.