I did exactly this with Komplete
I got the Ultimate edition, which came on a small SSD drive - but it doesn't run from this drive so it still needs to be installed
What you want to do is download and install the PROGRAMMES to your internal drive (they are quite small) but install the Komplete LIBRARIES (which are HUGE) to your external external drive
From memory you get a choice of where to install each component
This vid should sort you out:
Good luck and have fun with KOMPLETE - I think you would only ever scratch the surface in a lifetime!!!!