But a serious answer to the original question;
I used to live right near the Como Pub on Canning H'way (god awful old Main Roads Dept owned Rental *shudder*) and commuted into the city. Most directly it was 5Ks over the narrows. After a while I started hooking away from the city, through the 'burbs and coming out on the Freeway bike Path anywhere south of the Como Jetty and then turning back towards the city from there.
I think I peaked at about 25km one way coming out at the last pedestrian overpass north of the Mt Henry Bridge, heading over the Bridge, then loop back North again on the west bank of the Canning in Mt Pleasant, skirting the Raffles, back over the Canning Bridge and North into the City from there, over the Narrows etc again.
I reckon if you cut through St James/Curtin/Manning/Mt Henry you could have some nice extra distance and still have the nice extra run along the river. Google map the possibilties
