Can the Galaxy S2 be rooted without increasing the custom flash counter using adb? Normally, rooting guides for the S2 involve flashing a kernel to the device to install busybox and su. This xda post suggests a method for doing so via adb (found approximately in the middle of the first post):

adb shell mount -o rw,remount /dev/block/mmcblk0p9 /system
adb push busybox /system/xbin/
adb push su /system/xbin/
adb shell chown root.shell /system/xbin/busybox
adb shell chown root.shell /system/xbin/su
adb shell chmod 755 /system/xbin/busybox
adb shell chmod 4755 /system/xbin/su
adb shell /system/xbin/busybox --install -s /system/xbin
adb shell mount -o ro,remount /dev/block/mmcblk0p9 /system


This also seems to be the method tools like SuperOneClick use. Now I recently found this blog post indicating the above method does not increment the hardware counter in the S2 that counts flashes of custom firmware. More than that, it can also be used to install ROMs via Mobile Odin, also without increasing the counter, because they come form the device itself and not from a computer via the USB cable.

I fear to try out myself and lose my precious counter value of still 0. Has anyone tried out a method like this before and can confirm that it really does not affect the counter?
You can make or buy a USB Jig for Samsung Galaxy S2 i9100. It’s a really simple circuit that involves putting 300K Ohms of resistors between pin 4 and 5 of the microUSB connector.

With a USB Jig you can reset the custom binary counter to zero and also remove the yellow triangle on start up if you have rooted your device. 


Turn off your phone completely and remove the battery for 10-15
seconds 
Put the battery back but don't switch on the device 
Plug the USB Jig into Micro USB port of your phone Wait for around 2-3 seconds
You phone screen will show "ERASING DOWNLOAD INFORMATION SUCCEEDED" in ODIN mode and Custom Binary Download : No
Now you can remove the battery and restart the phone.You will also notice that the yellow triangle which comes at start-up is gone now.