Merging columns in Visual Composer

I am using six rows to create my homepage. The rows are split in either two or three columns with the last column meant for the sidebar. I am using the first (in two-column row) and first, second column (in three column row) to build the left panel. But I am not able to create a widgetised sidebar since I am left with six columns (the last column of each row). If I use the last column of the first row to place the widgetised sidebar, the remaining five ‘last columns’ are still left unused. Also, the left panel of the first row height is automatically increased to the height of the widgetised sidebar, leaving a huge blank space until the end of the height. If I am able to merge all the six last columns into one, and use it for the widgetised sidebar, my problem will be solved. How to merge the columns into one? Anyone please help. Thanks