i agree with bugs the spot over the runout area is a better option & it will not hinder the downhill schedule, i skated it 3 weeks ago, its not bad...

Been thinking....(my curse!)
I reckon there could be 3 "slalom side-show" events.

Day 1) The Eddie Spearing 100 Cone Challenge. 

Course set on mountain straight, behind the finish line, to where the buses turn around, and only using half the track, so ambulance and service vehicles can get through OK,  like we did in 2008.  No start ramp needed, just a timer and cones,  loan boards, deckchair and clipboard...oh and a money jar.  Could be run by 1 or two people.

It can run all day without interfering with the main event, and downhill racers can have a crack at it between heats or after they are eliminated.  And course marshalls can get a go and use it to set a time during their lunch break. 
This will help everyone get their wiggle happening for the next event on the following day!

I would also make sure that there is a Penny board available for the 100 cone challenge - because that is what the next generation of slalomers are riding right now - and Penny will probably kick in with a prize - besides you lot can skate anything...can't you!

$1.00 per run, fastest clean run wins the 3/3 of the cash, fastest Penny wins 1/3 of the cash (or what Penny provide)

Everyone who wants to do head to head could set a 100 cone time for their ranking so we can save the time normally used for qualifying for the head to head race.

Day 2)  The Conrod Cup

Lunch time head to head on Conrod Straight. - between the run-out and the chicane. 
Racers "start rankings" can be set by using times from the 100 cone challenge, in order to save qualifying time on the day.
(if racers can't get to Bathurst in time for the 100 cones, their 2012 ASRA ranking could be used)

 
Track verge is wide enough to get the buses through providing it is not wet, and that area retains a good connection with the main event, so that racers waiting for the next bus can see it. 

Non downhill racers $20 entry, downhill racers & track marshalls free - ASRA points and a new set of bearings for 1st 2nd & 3rd.

Day 2 and 3) The Forest Chase GS

Longboard GS Forest Elbow to Conrod finish line - after the main event has finished - Day 1 practice, Day 2 Race.
free to downhill racers  and track marshalls. 
(if downhill racing finishes at 3:30pm, there could be about 1 hour of GS racing before handing the road back)

Could be single lane with transponders for continous racing or head to head with the trackmate.

(will need a motorbike to get the transponders back, and a clamps to fix transponders to boards, Retro Racer, are you interested in helping with this???)

Don't forget this is all a side-show to the downhill event, and should not be run in a way which interfers with the operations of the downhill race, however it should be run in a way which ,makes it easy to organise and open to as many as possible. 

Hope this helps!

So given time and access, option 1 is it.

Skyline has also had Head to Head slalom at the 1st Bathurst Downhill.