If you have the budget, you could try something like this:http://www.mfjenterprises.com/Product.php?productid=MFJ-1786
Not exactly unobtrusive, but then an HF rig won't be very stealthy either -
you won't be able to run QRP with this kind of antenna, but you will make contacts.
Be careful of the RF energy exposure ...
you might be safer to make a loop dipole for 6 meters our of copper tape, and use 50.125 SSB from something like an Ft-817 or a small 6m rig - http://www.mfjenterprises.com/Product.php?productid=MFJ-9406X
with your 8th floor height, and listening with squelch, you just might catch some fun openings....