vnoremap > >gv
Now highlight a column of text using blockwise visual selection (ctrl-v on Unix platforms, ctrl-q on Windows) and then hit > or <
>>>> (would shift four shiftwidths to the right)
You can also use traditional ex mode to accomplish the same. Go to the first column of a given block and type ma (in normal mode) to set mark a. Go the the end of the block you want to indent, first column, and set mark b by typing mb (in normal mode). Now issue the following ex-command.
:'a, 'b>> (shift two columns to the right)