Populate report control on demand

I'm new to these controls and am trying to work out if there is a way to populate the report control on demand, when using the report in tree mode or list mode with grouping.

For example I have a list of parent items and each parent has a list of child items. I populate the list initially with 1 child from each parent (this is just as a holding item so the parent is represented in the list) and group the list by the parent name.  After calling Populate I then collapse all the group rows in the control and show the form, so i have a list of collapsed groups which the user can then choose to expand.

Then when the user expands the group row i want to retrieve the rest of the children for that parent from the database and add them to the report control. I've done this sort of thing many times before using a standard tree control.

There is no "Expanded" event  that i can see, even when the control is working as a tree. This would be *really* handy.

I have experimented with using the "BeforeDrawRow" event to catch that the "holding" item is about to be drawn and then retrieve the items from the db. If i then call the "Populate" method from within the event handler it crashed vb with a "memory could not be read" error.

I'm really impressed with all of the controls in general, but really need to be able to populate the report/list/tree on demand. It i can't do this it may sink some of my app designs.

Any suggestions or help would be appreciated.

thanks