current limiting filament bulb, revisited
100W 12.8Vdc bulb
R(hot)= V²/W [Ω]
 R(hot)  = 12.8²/100W  = 1.64 Ω , 0.16 cold, 0.5 ohm dim?  ( verify?) 
Cramp Amp rating is done at 7.5V , you are getting 8 or 9V.   

Thus for Glow plugs load during hard starting I would suggest your setup with 100W in series is a reasonable simple solution.

If you want more voltage into the glow plugs, say so...

Impressions:

I think the boost pack is intended to fast charge the dead battery in minutes but not directly run the starter motor in the cold at 500 CCA.
Adding the 100W lamp only supplies a small percentage of power to the glow plugs and starter motor during the actual start, while no current limit triggers the overcurrent warning.  You may correct me if my impression is wrong.

I think if the LiPo boost pack charges a cold battery with 100Amps that if this raises the electrolyte temperature it would be useful to restore the cold battery ESR and efficiency.