I am a huge advocate of what you propose. I have 3 different size road morphs, one on my road (mini) one on my commuter (mountain) and one on my fixie (regular.) I use the water bottle boss side clip for all. I hate zip ties so much. The regular Topeak mount is really ugly and destroys teh lins of your bike.

I got my holders through Performance Bike. Last time I looked they didn't sell them any more.

I looked on eBay and found several by searching for "bike pump clip" I think that will work for you!

I know the one I have was a bit large for my mini morph. I put a wrap of tape on it and it now fits perfectly. I also use a velcro strap just for good luck.