I am researching for the same problem (Android 2.3, htc wildfire s), this are my investigation results:
It works! Unfortunaly it works, if you connect the phone without accumulator and after that insert the accu- now its autoboots. Connecting the phone with inserted accu or insert the accu in the unconnected phone does not work.
Not the result I hoped for but maybe a hint for a pointer.
And I found a script solution: https://android.stackexchange.com/questions/39899/auto-boot-when-charger-connected-for-htc-magic
echo "echo skipping chargemon" > chargemon.script
adb pull /system/bin/chargemon chargemon.backup
adb push chargemon.script /sqlite_stmt_journals
adb shell
$ cd /sqlite_stmt_journals
$ su
# mount -o remount,rw /dev/block/mtdblock0 /system
# cat chargemon.script > /system/bin/chargemon
# chmod 755 /system/bin/chargemon
# reboot -p