Tool Storage Bag for Mini 4?

[TNOutback]

I'm having trouble locating a small frame bag where I can keep a set of bike tools, spare tube, etc. on a Mini 4 that does not have a rack.  An under seat bag would interfere with removing the battery.  I've tried a frame bag that attaches to the base of the handlebar stem with velcro, but the base of the stem turns with the handlebars.  Any ideas or recommendations that does not involve getting a rear rack?