Mounting any sort of optical finder is going to be a PITA without a shoe.
Options as I see 'em:
- if there's enough room on the camera's top plate -- ideally precisely over the centre of the lens -- add a shoe (search for "cold shoe" -- about $15), then add an optical viewfinder (with all the caveats already mentioned about zoom, parallax, etc.). Unfortunately a suitable optical finder may not be as cheap as you'd like. I'd look for a finder almost as wide as my camera's widest setting, but there's nothing stopping you from trying out various lengths
- get a shade for the LCD, assuming your main issue is that the screen is hard-to-see in bright light
- get a loupe, e.g. a Hoodman. This basically covers your LCD with a little tent; you look in through an eyepiece
- trade up to a camera that solves the issue without any further fuss or hacking. My preferred option, but one of the above hacks might work for you.