Within the datagrid2 i for sure know that there is a functionality for that( see below), but i think it is also available for datagrid1, if i remember correctly:
I dont think this possible for datagrid. The closest option to what you want to achive with datagrid is to fillout a Default value.
But in order to get the desired results, the advice of Jelle to use datagrid 2 is your solution.
Good luck with it.