This may be what you are looking for:
http://technet.microsoft.com/en-us/library/bb123962.aspxHow to Manage Segmentation in Outlook Web Access
http://technet.microsoft.com/en-us/library/bb123515.aspxSet-OwaVirtualDirectory
RecoverDeletedItemsEnabled
This parameter specifies whether a user can use Outlook Web Access to view, recover, or delete permanently items that have been deleted from the Deleted Items folder. By default, RecoverDeletedItemsEnabled is set to $true. If RecoverDeletedItemsEnabled is set to $false, the items deleted from Deleted Items are retained. But users cannot view, recover, or permanently delete them by using Outlook Web Access.
If however, you are looking to ensure users can never delete anything from the Deleted Items folder itself, than, no. In that case you should explore archiving or journaling to preserve all the messages or perhaps look even at Exchange 2010
http://msexchangeteam.com/archive/2009/09/25/452632.aspxSingle Item Recovery in Exchange Server 2010 .