Assessing and reducing EMI from PWM LED lighting
You might not be able to use the "data-over-mains" solutions that are designed for AC power lines, but there are a lot of DC powerline communications products available, too. If you poke around enough, I bet that you will find a match for your application. 

Here are some examples, although neither quite explicitly says that it supports 48V. 

FROM TI: http://www.ti.com/tool/24VDCPLCEVM

FROM CYPRESS: http://www.cypress.com/?id=2330&amp;rID=39248

"The CY8CPLCXX enables control of Automotive LED strobe, beacon, tail lights and indicators over the existing Direct Current (DC) 12V-42V Battery Powerline."

There are lots of others. I would probably advise against spinning your own option 1 based solution, unless you are a really confident analog designer. I would advise against an option 2 based solution, for both EMI and SI concerns.