I managed to find a work around for this problem. I did this by creating a "dummy" icon which was basically a square with the same colour as the background colour of the tabbed panes. I then set this icon as the icon for a "dummy" tabbed pane and disabled the tab:
jtp.addTab("", dummyIcon, null);
jtp.setEnabledAt(0, false);
By resizing the icon I could make the first tabbed pane take up as much space as i wanted since the panes don't have to be the same size. This way The first tab was not clickable and it had a colour similar to the background colour of the panel, so it appeared as if the space was empty.