Robert Reed, who played Mike Brady on the Brady Bunch, complete with the big white guy 70's perm. Of course, he's dead, so I'll go with Gary Cole, who played Mike Brady on the Brady Bunch movie, complete with the big white guy 70's perm.
Vulcans/Romulans don't have perms. They're illogical. But all kidding aside, Gary Cole might've worked.
I still like the Romulan dad angle. Even though it would've made T'Pol more like Saavik was supposed to be -- as I don't think Saavik's part-Romulan heritage was ever revealed onscreen -- it wouldn't have to account for her less-than-perfect emotional control.
Poppa T'Pol could've been a Romulan agent who eventually "goes native" and embraces the Vulcan way, turning his back on the Romulans. The Romulans then try him in absentia and assassins kill him. T'Pol could unearth a diary from her father he hid with instructions that it eventually be presented to her.
To preserve canon, she would only confide in Dr. Phlox the secret of her father's true identity. The pretext: Phlox finds traces of a genetic flaw that led to T'Pol being more susceptible to Trellium-D, but he has never seen this anomaly in the Vulcan medical database. This would fall under doctor-patient privilege.
Armed with this new information, Phlox speculates that T'Pol's part-Romulan heritage is responsible for this susceptibility to trellium-D. And even though at this point, no one knows what Romulans look like, Phlox and T'Pol realize all the evidence points to Romulans being almost indistiguishable from Vulcans, with minor differences, which would explain the legend of Vulcans who left the homeworld thousands of years ago under the banner of the Raptor's Wing.
Then, T'Pol reasons if Vulcans and Romulans are related and look alike, revealing this to Starfleet would set back Vulcan-Earth relations, so she shoulders the burden of this secret, keeping it from Archer and the rest of the senior officers.
Hey, it isn't any less far-fetched than the whole Klingon smooth forehead story!