Hey @
Heathpack, the two best options for a frame mounted pump are either under the top tube or alongside your downtube. Several pump makers make a plastic mount that essentially allows you to run a pump side-car along your bottle.
Also, I highly suggest you practice using your C02 at home a couple times so you are comfortable with the technique. I am a cheapskate so I bought a dozen of them from Walmart for around 8 bucks. That way I did not feel bad using a couple to learn on.