How to ask for an Accelerated process?

Hi monkeys,

I am fortunate enough to receive a summer internship offer from a top bank. However, I do also have an upcoming final round with my dream bank (direct competitor) in late next week. The offer I have in hand explodes soon. The people at that firm were great, interviewees called & emailed congratulating for offer, so I wouldn't personally feel okay signing and reneging a few days later. How would you compose an email asking to accelerate my process? Any advice or even email template would be greatly appreciated!