It doesn't appear to work like that on the ABS modulator on the BMW as I have changed the lines on mine, changed fluid numerous times, changed the master cylinder and calipers and have never had to activate the pump like you are talking about with cars.
Generally I tend to use a mityvac to drain and sometimes to bleed fresh fluid through and when that doesn't work I also reverse bleed using a syringe to pump fluid in from the caliper end, on the BMW I haven't bothered and instead just filled up and bled as normal, it took slightly longer to get pressure given how long the route is for the front calipers going via the seat area and then back to the front wheel but the fluid bled through spotlessly and lever is solid.
This lever coming to the bar though is a common enough problem that I have found other people complaining of and generally on standard braking systems (all tends to be ABS too) so the only thing I can thing of is air having been trapped in the the system somewhere in the ABS modulator, it happened to me on a number of occasions and I mentioned it to BMW when it went in for its second service as they were going to be doing a fluid change (because there was no record of it having been done on the first service apparently). They said they had never heard of the problem although it's easy to find on the internet.
Regardless even with a fluid change at BMW some days later it did it again exactly as described above, pull the lever first time and nothing, a few pulls and full strength brake lever which could remain like that for days, weeks or quite randomly it could be gone the next time you pull the lever after it has been stood for a while.
It could possibly be a smidge of air trapped in the master cylinder but I am inclined to rule that out on the basis that generally when air gets trapped in there it feels spongey all the time whereas this for me was completely random and it never affected braking performance or lever feel once the lever was pumped a couple of times at switch on.
