Here is a quick and cheap solution.
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Signing UpStep 1: Materials and Tools
1 - thick wire coat hanger
1 - 1/4x20 nut
2 - rubber bands
Tools:
pliers with wire cutter
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You could bend the coat hanger on step 2 to fit a sidewards iPhone, or if your tripod allows you to flip the mounting screw so that it is horizontal to the base you would not have to change anything.