I took advantage of a fare error from CMB (you know, the famous CMB-SYD-JFK via Europe) a few years ago. To position myself I flew LHR-FRA (BA) then took the InterCity train with only a few mins to spare to get to DUS where I flew out a few hours later on Air Berlin to IST. From IST it was a 4hr flight to DXB on SIA. I then had around 5hrs in the UAE to transfer from DXB to AUH (mad taxi dash of about 100 miles - scared the wits out of me!) where I flew to CMB on Sri Lankan - all on separate tickets with one train and one taxi connection in between. I flew LHR-FRA/ DUS-IST-DXB/ AUH-CMB-SIN-SYD-MEL on 5 separate tickets with one train and one taxi transfer and all connections were under 5hrs.

Edit: And I only paid £10.00 APD.