I just checked the BMW shop manual, there is no specified torque value for the bolts .
I know you don't want to hear this, but it's a 'feel' you get with working with steel bolts threaded into an aluminum casting .
About the only advice I can give, is to get a 1/4 inch drive tool, that has a screwdriver handle, you can put 1/4 inch drive sockets on it and tighten them up .
The method I use, is to use my non-dominant hand to do the tightening .
Don't know if it helps at all !!!!
You can always tighten up a little more, if you have any oil leakage, kinda hard to untighten a stripped thread .