I have the ASUS P5Q Pro Turbo, with a Xeon X5470 onboard. I just did like you said with the adapter, and cut off some of the plastic guides.
You will need to modify the BIOS, but I have already done so myself, and can supply the ROM if you are still interested. This BIOS is v0701 (or latest version as of post date), and supports any CPU's other than the X5470 (which I think there are not any) that have a CPUID of: 1067A.
If you are looking to put a different Xeon on your board (which the 70 overclocks the best), I can modify the BIOS for whatever Xeon you would like that supports the P5Q. If I remember right you can do the E5450, the X5450, or the X5470.
And you do not need a modified BIOS to boot or run general programs. The main annoyances are 1) A warning everytime you boot. 2) No Visualization Acceleration for x64 and/or quad core virtual machines.