I believe you can set the state using the querystring eg: ?_state=statename.

However you are talking about sub form and the open subform rules dont seem to let you set this. I have see in the "navigate to url ", there is a "open in " option.

-Current window

-New window

-Parent window

-Modal dialog window

I think the option you can try is the "modal dialog window" option.Then just add a parameter called _base and set the value to the base name. I am not sure it will work that well with the subform rules though but you can try.

Hope that helps

In scenario using the "Naviagate URL", the events in the subform cannot be recognized by the parent form. I'm finding a better way to recognize the parent form when triggering an event in subform.