A system for use with a balloon having a balloon envelope is provided. The system includes a tendon assembly for mounting tendons to the balloon envelope. This tendon assembly includes a plate structure having a fill port attached to an apex of the balloon envelope and a plurality of tendons arranged over the plate structure. The fill port is configured to allow lift gas to pass into balloon envelope. Each tendon of the plurality of tendons has a first portion, a second portion, and a middle portion disposed between the first portion and the second portion. The first portion of a given tendon is arranged to engage a first section of the plate structure. The second portion is arranged to engage a second section of the plate structure opposite of the first section. The middle portion is arranged to wrap around the fill port of the plate.