I want to use ParentForm property for the businessObjects that is initiated in the code (i.e not dropped on the form) 

Currently, This type of objects has null value for the property. I've seen the other constructor (with parameter Icontainer) was working. But I couldn't understand When these properties were set. I may follow the same way.

How can I achieve this ?

I'm trying to get some business object usage information like Which forms use which objects for logging purposes.
If I know the parent object (especially the form), it will be logged with necesseary related information. After some time,
I will expect nearly to get some useful information for dependencies between forms and objects.

One thing you may want to use is the BusinessObjects property on the form.  The form has a collection of BOs on it that are dropped on that particular form, so you may want to try that.  But you will not be able to set the ParentForm property...this is a readonly property that sets itself.  You could look into the ParentContainer property, as mentioned in the previous post, as well.