What I did, was to soak a brush in laquer thinner and dip into the putty, like painters use oil paint and thinner on a palette. Worked just like surface primer on a brush.
On the other hand: I mixed primer and thinner 50/50 and tried airbrushing on a few parts. It seemed to work, but I had a heck of a job cleaning the airbrush afterwards. Maybe not surpising, as the primer is supposed to adhere to metal as well as plastic.
Do anybody use Tamiya primer with airbrushes?
I'd prefer to avoid the spray cans, as the mist goes everywhere. I just barely rescued my $300 per glass eyeglasses from the mist - and yes: protective goggels are now in place. Still, I'd prefer the fine control of the airbrush, if I can get it within reason.
Doc