My best suggestion, and be it I'm still trying to get 100% of the stuff before I get to deep into the track creation:
Try making a shortcut, starting from where the main track is to the ramp and then to the bridge itself, closing the shortcut.
Then, after adding the ramp where you want it, make the track invisible from the ramp to the bridge.
Hopefully this will stop that illegal shortcut notice. Also, sorry if this doesn't work or isn't what you wanted, I'm still learning.

you will need to make it so it is a secondary path and then make the jump bit invis so it is still considered a way to go 

Actually you can make "air breadcrumbs", and this is most likely what you need to do.  Once you place your breadcrumbs press L1 to get into the select breadcrumb mode.  Using this you can then select each individual breadcrumb node and using the raise tool (hold SQUARE and then use the UP or DOWN D-Pad) lift each breadcrumb node.  Make sure that none of the breadcrumb nodes are actually above your jumps "flight path" as that will still render it an invalid shortcut.  Hope that helps you out - if not just drop me (or any MNRHQ Pit Crew member) a line.  Later.