How dynamically set DropDownList datasource when in DataGrid?

[VB Programmer]

I have a DataGrid with a dropdownlist in one of the columns (it's a
TemplateColumn). How do I set the ddl's datasource dynamically via code?
I'm having trouble knowing how to reference the ddl.

(I know how to connect to the db, get the data, etc... I know how to set a
normal ddl's datasource. I just need to know how to do this when it's in a
datagrid.)

Thanks!