New ALV Checkbox functionality

I have an ALV Grid display using the Standard Function Module. I have the 1st column as a Checkbox. Now the Customer wants to have a functionality wherein If the User clicks on the 'Select ALL' button then all the Checkboxes will be selected & If the User clicks on the 'Deselect ALL' button all the Checkboxes should be de-selected. Moreover the Customer wants to have an additional button for partial selection. If the User clicks the checkbox for the 1st entry and then clicks on that button & after that selects say the nth entry & again clicks on the same button, then for all the n entries the checkbox should be selected. Interesting but not DIFFICULT!

Regards

Tanmoy