WIth the seat out of the car - Laid on its side..  

I used some padding (cloths or old shirts or something.) then a 2x4 chunk of wood to spread out the pressing area   Bottle jack in between.

The only issue i would have is if the pressing area wasnt centerd the 2x4's would quickly buckle Inward ( pressing against the seat vinyl) or popping out.. TOok a few settlings and extra set of hands to hold in place. 

I believe i measured 2 inches of spread- would retract right back to 1 inch of final gained width. You might be able to press it more,.

a fixture to hold the press blocks in place would be nice.

Or a Port-a_ power type presser would be just as good too. 

And now i remember- We did the same to my buddies cobra's that were mentioned above. 

Most if not all the aftermarket seats i have run across wear rapidly even the cars that only go to shows and are kept in the garage. Nothing beats factory seats for wear and tear but they probably do not fit as tight as you would like for your application. The only way i know to get them right is to buy used ones and recover/foam them with quality materials at a reputable interior shop.

I have the Cobras. They came out of a Japanese Rover import. I would NOT buy them again.
ALL the foam in the back and sides crumbled into yellow dust. I have just paid a motor trimmer A$150 to re-pad them both.

Others here in Oz have the same problem. MADMAT told me they even do this sitting in the showroom. Crappy foam the factory used. 

I have the Corbeau's.  They are extremely narrow as jedduh01 said.  My waist is around 34-36" and it is very tight.  I am 5'10" and the seat back is mid back, head rests in my shoulders.  I haven't used them very long so I don't know how well they will wear.

Jedduh01 what did you do with the bottle jack to widen?  How did you protect the seat material from ripping?

//www.trackhq.com/forums/f195/what-brand-model-bucket-seat-you-running-4320/

I'm looking at Corbeau and Cobra Bucket seats for my 70 Morris. Can anyone tell me if the Corbeau seats are more or less comfortable than the less expenseive Cobra seats? Build quality comments appreciated. Thanks.

I should add that these are street use only with a few Autocross events.