I'm sorry but I'm not able to make more complicated and realistic simulation atm. Something wrong is going with my computer - CPU is overheating and I had to restart computer twice making this tutorial. Calculating more complicated simulation would crash it again I'm sure.

To obtain more realistic effect:

• In step 5 pose cloth rotating it along z and y axis (I rotated along x only).

• After loading obj (step 2), unzip band on the back (ripp it). How to rip clothes I've explain here:
  http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3322264
  In your case it is easier, because you must ripp only one mesh.
  Of course delete imported obj and use ripped prop as a dynamic cloth.
  With ripped cloth you can use square. After first calculation change simulation setting and add 10 frames to animation. In fame where bra is laying on square (as in step 6) add keyframe. in last frame of simulation strech square along x axis. Remeber in clothing room check box "collision friction". Increase either frictions in "_default" group. It not strech straps as much as it was shown on your picture but some effect should be visible.

• If you wish obtain effect shown on photo 3 - 4 you can do it very easy. Go follow steps 1 - 4 and in clothing room select "choreographed" group (see picture - top of right arm, almost invisible). Add few verticles on the strap and calculate simulation.