There is an existing vehicle track which leads from east of the car park (currently fenced off on the western side) past the western side of the RMS facility to almost the sewer. Judging by the condition of the track compared with another foreshore access track, it is not used much by vehicles. This track could be turned into a path which would function mostly as a bike path without ruling out occasional access by RMS vehicles (there isn't much RMS vehicle traffic, so there should not be a problem).
Below is a picture of the access track at about the point where the bike path needs to get onto the sewer.
Below is a picture a little bit closer to where the pipe crosses the sewer.
The first picture is looking south and the second picture is looking north.
The abandoned concrete chunks and steel beams would obviously have to go. The fence and gate are unnecessary and should also go.