Leads 'Unread By Owner' - Need a Workaround Please!

[Lacertosus]

Greetings Community, 

I’m trying to create a workflow against the Leads object that would fire off if the lead owner has not read/open the lead after so many days of it being assigned. Workflow would then send an email to the lead owner as well as manager stating that a lead has not been read. According to SFDC the ‘Unread by Owner’ field is a ‘system’ field and is only available via views on the Leads object. No workflow can be built against it. They recommended that I base the workflow on the ‘Last Modified Date’ even though they do agree that the proposed workflow would not be that accurate. Can you please assist with a suggestion on how to approach? Thanks in advance