To use (run this in your GDB prompt or add to .gdbinit):

python import sys
python sys.path.append('/path/to/offsets.py')
python import offsets
offsets-of Whatever

If you're making changes to it, the following might be more useful:

python import sys
python sys.path.append('/path/to/offsets.py')
python import offsets
python import imp

Then every time you make a change:

python imp.reload(offsets)
offsets-of Whatever