I really don't know the name of it...I think it's a putty from Gaia or the brand called (i guess) Finishing products for professional (that also makes great paints BTW) or something,but in the end use the tamiya one and you'll be doing great. You can use the Gunze harder one which work a bit better than the tamiya one but I think it will work anyway.

Ohhh and btw...I suggest you to try thinning down the milliput and have it like cream consistency and try to do the same work...I discovered this for filling gaps and works awesome!

Maybe you can use it for the same purpose as shown here in the vid!

Hope this helped

Cheers