On the two cars I've had with Comfort Access, if you lock the car from the outside, open the trunk, then put the key fob in the trunk and close it, the trunk will re-open. I'll try this with my 550i when I get it (which will hopefully be this week, assuming it didn't get flooded out by the hurricane when it hit the VPC in New Jersey).
'11 F10 550i M Sport (ED Aug 1, 2011; US deliv, Sep 12, 2011)
'08 E90 M3
'07 E92 335i
: ordered Nov '06; delivered Jan '07, totaled Sep '08.
'02 E39 M5
: June 2002 - June 2007
'00 E39 540i/6
, '97 E39 528i
, '92 E34 525i
+ VW, MBz, Peugeot, Toyota, Olds