I looked for this same answer a while back and determined it was silly to do such - mainly because the only way around it IS to build everything by hand.
rails g scaffold TableName --skip-migration field:string field2:string field3:string field4:boolean
That's going to be the only way around it. And you may have to explicitly define the table name if it doesn't match rails naming structures. Any way you spin it, you're going to have to redesign forms for the data anyway.
Check into the formtastic gem - it might aid you in building forms from scratch. I believe there's a Railscast on it as well.