Adding Multiple item to item groups

Adding Multiple item to item groups

Hi,
how can I Add Multiple item to item groups. Each time I add a item to item group, it takes me to item group page. Then I have to navigate again to items page , again select only 1 item and repeat entire process over and over again. Only way to add multiple item in a single group is to , when you are adding new item inside group. What about existing items? what if I want to add multiple items already there in inventory to a group?
how do I achieve that. kindly provide add on feature for this on urgent basis.