You can get a reference to the folder in code without selecting it, then
instantiate a specific form and display it using something like:

   Dim objMail As Outlook.MailItem
   Dim objInbox As Outlook.MAPIFolder
   Dim objNS As Outlook.NameSpace
   
   Set objNS = Application.GetNamespace("MAPI")
   Set objInbox = objNS.GetDefaultFolder(olFolderInbox)
   Set objMail = objInbox.Items.Add("IPM.Note.MyCustomFormName")
   objMail.Display
   
   Set objMail = Nothing
   Set objInbox = Nothing
   Set objNS = Nothing

You can access other folders by working through Folders collections in each
folder.  i.e.
objMail.Folders("InboxSubFolder").Folders("InboxSubFolderSubFolder")