Fstab mounting fails when remote share is OFF
Not exactly what you asked for, but at least your boot won't hang when the remote is down. Otherwise you'd need to write a short script to check for remote up, and then mount share.
Edit your /etc/fstab and try adding nofail like the example I show below...
//caspurr.local/usb_storage /media/my_username/caspurrshare cifs nofail,gue
st,uid=1000,iocharset=utf8 0 0