I have done this! It's harder/more stressful than you might think, but it's absolutely possible. We installed relay radios powered off the photocell plugs to bring low-speed internet to a family friend's farm, so the actual installation doesn't even involve wires between poles, just shims under the streetlamp photocells. Presumably they'll get knocked out when the streetlamps are upgraded... but it's been six years so far with no issues.