BCGControlBar Pro for MFC
void CBCGPMDIFrameWnd::EnableMaximizeFloatingBars ( BOOL  bEnable = TRUE,
BOOL  bMaximizeByDblClick = FALSE,
BOOL  bRestoreMaximizeFloatingBars = FALSE 

Specifies whether a maximize button should be displayed on the floating control bar caption.

bEnableTRUE - display the maximize button, FALSE - hide it.
bMaximizeByDblClickSpecifies whether the floating bar should be maximized by left mouse button double-click. If this parameter is FALSE, double-clicking the floating bar caption docks the bar to the previous docking location.
bRestoreMaximizeFloatingBarsSpecifies whether a maximized docking bar should be maximized again in the next application run.