Either a universal sandwich plate from ebay, you'll need the M18 variant, or a T-piece on the oil pressure gauge, with an M14 thread.
I actually ventured down this route last year with some Mocal Oil temp/pressure sensors taken off a 3 way T-piece and its a tight fit down there but i managed to fit them all up. You may find it a better option to get a sump plug with a sensor thread in the middle for temp. I tried this but on my car ground clearance became an issue as my sender unit was quite long.
Removed the setup because A) i missed my radio slot, and B) no matter how hard i pushed it for how long the temp never seemed to fluctuate to a noticable amount.
The only advantage to such a setup is you know when your oils warm enough to thrash it. Obviously as a failsafe measure oil pressure is always handy.
Sandwich plate option is probably the easiest, you can then fit multiple sensors to the same plate.. i.e. oil pressure + temp. Some can be a PITA to get sealed well though, then you have the whole clearance with the radiator.
There must be an oil temp sensor on the car for the ECU to read, on all cars. The RS Monitor reads in OBDII data, so you could just get something like a ScanGauge to show you this instead.
Yeah, i was thinking the same thing. if you could just extract this data from the ECU it would be easier than putting a seperate sensor in to do the job. i'm going to have a nosey at this and see..