80 seconds fast then 40 seconds SR (so 2 mins per unit). 
Use the 'bottom of the tan', starting clockwise from the Pillars. Run two reps out then two reps back and regroup at the Pillars before the next set of four.

The famous Milers 100 x 100m Christmas event (non-points scoring)- obviously you can opt to run less than 100 reps. Alternatively run some 600s (6-8?) off 3.30.

This is a variation on the Double Pyramid session. Run from the Pillars to the 750m mark, then 500m back towards the Pillars and then 250m to return. The tempo of each set picks up as the distance decreases. Complete three sets in total. 
Recovery: start on 4.30, 7.45 and 11.00.
[Alternative session: skip the last set or scale it back e.g. finish with 2 x 500m or 2 x 250m.]

New course:1500m (on 8.00), 2 x 1000m (on 5.15), 750m (on 4.15), 500m (on 3.15), 250m. 
Start at the pillars. Run to the 750m marker and back (1500m), Regroup at the Pillars and run to Government House Dr (1000m), Return to the Pillars (1000m), Run to the 750 marker (750m), then back to the 250m marker (500m) and finally run the last 250m to complete the session.

8 x 3 mins with 1 min SR. Run along the river and turn after the 4th rep.This is designed as a threshold session but can be run as a regular interval session if you prefer.
Alternatively, it can just be a 32 min steady run.

Run out and back using the 500m marker. Start the second rep 3.15 after the start and so on.   Alternate session: Reduce number of reps to 6 or 8 (skip the last or first few reps)

Start each set (i.e. odd rep) at the Pillars.1) Run for 2 mins clockwise, wait for 60 secs, return. Re-group at the Pillars. 2) Run for 5 mins anti-clockwise, wait for 60 secs then return. 3) Run for 1 min clockwise, wait for 1 min, return. Repeat. Recoveries are all 1 min stat rec.  Options: (a) skip a set or two to reduce total volume.  (b) increase the 1 min reps to 75 secs (and take only 45 secs rec) to reduce intensity.