If you have an oscilloscope, you can view the coil firing and injector firing waveforms. That will help determine whether it's a bad driver in the ECU or maybe just flaky wiring.
There are several threads on cylinder 5 misfires. Seems to be a common problem. Just had another 335i w/ PPK tune only throwing misfires on 2 and 5 on cold start. That one might be a simple injector issue, will find out next week when it comes back.
So - the problem might be crankcase vent (PCV) related. Themyst has commented on valve cover gasket issues, and Rob Beck has developed an upgraded PCV valve for $45. Might want to uprade to the Rob Beck PCV valve (which just happens to sit right on top of cylinder 5 in the valve cover) and replace the valve cover gasket. Also use a high quality sealant on the gasket around the ports from the PCV in the VC to the cylinder head. It is plausible that a leak can suck lots of excess oil into the ports, especially cylinder 5 due to the location of the PCV valve and the channel that runs into each individual intake port.
My ports were quite wet with oil, and there were black tar balls on the #5 valve stems - this is after only 15k miles since I last cleaned them a year ago! Looks like PCV could easily be to blame for the oil, and possibly the cause of weird misfires that seem to be most common on cylinder 5.
E92 335i/6MT Dinan Stage 3: intercooler, oil cooler, intake, flash, exhaust, LW dual-mass flywheel.
Vishnu PWM methanol custom trunk mount, Diffsonline 3-clutch Salisbury custom diff, Ohlins Road and Track coilovers, Vorshlag camber plates, much more...
E28 M5 w/ buncha stuff, R171 SLK350