Step1
What I have done in the past to establish a higher track count is to create "stems" of certain elements within the session.
In the old days we had to strategically make available one or more tracks that would act as the destination for the additional tracks. It was never pretty. The generation loss from bouncing around all these very essential elements of the song were horrific. This would result in poor sonics.
With digital we are able to retain a greater control of the sonic result.
Step2
Determine which elements you intend to bounce.
For instance, take all of the background vocals and "pre-mix" them, only balancing the vocals specific to the arrangement with volume and panning. You'll want to have a bit more control when mixing, so try to refrain from including any processing if possible.
Step3
Solo only the background vocals as you have now created a good blend among them.
Ensure that there is no clipping on the Master fader and it is set at "unity gain." In most cases the vocals should not be peaking beyond -9dbFS.
Step4
Highlight the regions containing all background vocals. You may also want to allow a bit of room at the head and tail of the regions.
Under the file menu in ProTools LE click "Bounce To Disc."
When the menu appears, ensure that you bounce as a stereo .wav file and also name the file "Background Vox."
Once the bounce has been established you need to send the file to a destination. When prompted, locate the session from which you are working and create another folder called "Stems." This is where you will send the bounced file.
Now press "OK" in the "Bounce To Disc" window.
Step5
Once the bounce has completed, you can now deactivate the tracks used in the bounce by selecting the tracks and right-clicking "Hide and Make Inactive." The tracks will still exist within the session, but will no longer be active, effectively freeing up more tracks. You can now hide them in the Track View window located on the far left side of the Mix Window.
You will need to import it back into the session by choosing "Import Audio" from the File menu.
Locate the new background vocals stem and choose "Add" and "OK."
Upon importing the track it will ask if you wish to add it to the region bin or create a new track. Select "New Track."
Step6
Now the new stereo track will be created for the background vocals.
If you initially used eight tracks for the background vocals, you have now made six tracks available. The stereo track will comprise two tracks (left and right).