It took a little bit of digging, and it turns out that there is a singular-ish library function (accounting for curvature, geometric, projection, location & mathematical assumptions) that helps add a distance to a specific surface position.
Function: ST_Project
Used below:
SELECT ST_AsGeoJSON(ST_Project('POINT(longitude latitude)'::geography, offset, radians(orientation)))
It's from PostGIS and therefore useable in Ruby/Rails, although not yet as native Ruby objects (gems haven't wrapped it yet), but as a PostGIS query instead.
offset
is in meters. orientation
is in degrees ('N'=0, 'E'=90, etc.)
Hopefully, this solution helps others looking for the same thing.