Auto populate form after opening via OpenURL

Auto populate form after opening via OpenURL

I have a Vacation request form that allows the approver to approve/reject via custom actions in the report view. Upon Rejection, I have enabled a form called "Reason for Rejection" to open. On that form, there is a Request Number field and a multi-text field labelled "Reason for Rejection". 

Is there any way for the Request Number field to auto-fill upon selecting reject? There is obviously a corresponding Request Number (Auto-number) field in the Add Leave form.