Combat Engineer with flamethrower?
And there's no way to stop flammenwerfer HT unless your opponent is hopeless incompetent. It costs way too little fuel and munitions (which is fine) to be realistically deniable.
Guards, mines, and mark vehicle are all very effective at keeping the halftrack away until you reach either T3 or T4.
You can easily have a flamewagon out before he has Guards. Especially if he's spamming maxims, as his cps will be lower than a heavy conscript start. Also, if he's heavy Maximing, he doesn't have Guard scout cars. You can easily micro your flame HT away from Guards on foot, especially if you have smoke (which makes early Zis guns useless outside of barrage).
Engi flamers aren't touching Pgrens, which you can have out in like 3 minutes if you're rushing Flamewagon.
There is a reason the recent tournament was dominates by clowncar spam, not Maxims. Maxims are really good and I think they can be worth back teching to, or T1->T2 if you can properly deny fuel and get early map control. But rush spamming them is easily counterable since Soviets basically cede their early game cap power.