Transition from Pooled IP to Dedicated IP

We are hoping to transition from a shared IP to a dedicated IP to optimize our email deliverability rates. Moving to a new Dedicated IP will, however, require a gradual IP warm-up.

I was initially hoping that during this warm-up period, Marketo would allow us to use our dedicated IP to complete the warm-up, but also "toggle" to the shared IP so we can continue business as usual sending emails to large groups of people during the warm-up. I was told by Marketo that this is not possible, and once we switch to the Dedicated IP, we will no longer have access to the shared IP.

My question is this -- does anyone have any recommendations for completing an IP warm-up so we can move to the Dedicated IP, while still deploying large emails during the warm-up period (which Marketo recommends we run for 6-8  weeks)? I am unsure how we can exectue the warm-up while still conducting business as usual in the meantime with necessary email comms.

Thank in advance for any suggestions -- any ideas are much appreciated!