"are there any diocesan synods for young people to speak and bishops to listen? They need to include young people who are only "occasional" Catholics, not just those always active."

Well, about 95% of students at Catholic secondary schools don't attend Mass very often, (who can blame them in the current situation, especially the abuse scandals). So forums at the schools would be a good starting point.

As for Catholic Clubs at colleges and universities, a lot of them are FTTM/traditionalist (depending on the backwardness of the local prelate), so they are of limited use, sadly.

Check out the Youtube video for Sydney University Catholic Society - a picture (or video) says a thousand words. 
Link: https://www.youtube.com/watch?v=93Gq0aSvPko

At 0.30 minutes you will see - wait for it! - Cardinal Raymond Burke with his red cape (he's a bit underdressed by his standards in this scene). 
Just the thing to appeal to university students!