No, you can't have a tab greater than another one in a single panel.
But you can hide the borders of all the tabs, so that the user can't see the borders of the Tab Pannel and changing the TAB will seem like changing the layout.
Try to play with pen = 0 pt,embossed effect set to none, color set to transarent or a variation of these effects.
how do you set the color to transparent?
While in Layout Mode, select the Tab Panel and use the Fill tool, choosing the middle button and then the first icon.