Is this possible in Windows ?
In OSX I can go to /Volumes/Usbvol/Thisdir .
Can i navigate to the USB volume without using the assigned drive letter?
Out of curiosity, why are you trying to do this? If it's because the drive letter changes and you're trying to access it across sessions, you can manually set it to something high like R: or Z: so that it won't be re-used by going to Administrative Tools -> Computer Management -> Storage -> Disk Management and then right clicking on the drive and clicking Change Drive Letter and Paths.
I'm not sure if it is consistent when you remove and re-add the device, but this might be helpful:
In Windows, this is generally not possible unless you've mounted the drive at a non-standard location.
It is possible to mount drives within one another starting with Windows 2000.