On the 128i, you can use the service menu on the OBC/BC to access the coolant temperature among other things. Follow the instructions below to get to menu 07:00 which will show the coolant temperature (a.k.a. KTMP-MON).
http://e90.wetpaint.com/page/BC+hidden+menus
No idea how accurate or buffered the values are. Would be great if someone with an OBDII scanner can confirm the values are actually real time and match the OBDII values.
Takes me about 10 minutes driving under 3k RPM to get to a stable temperature of 100C.