"Let me fuck your tits"

I suggest.

Millie looks a bit surprised, so I add:

"You just need to pop your tits out for that, so we can finish up pretty quickly."

Millie thinks a little bit, then says:

"I am not sure, why..."

I interupt her by saying:

"Look, I want this to go well too, but seeing your tits like you have them today is giving me a hard-on and I am not sure if I can concentrate now."

Millie gives me a sceptical look:

"So you are saying you need to tit-fuck me so you can concentrate?"

"Pretty much, and it is also an advance payment for joining you on this mission."

Millie looks at me for a few seconds, then pulls her sweater over her head, revealing her amazing tits, and says:

"Let's get started."