Spread O vs. Cov. 4

This week we are facing a team that runs a 3-4 with a cover shell. They will rotate safeties and play games with outside backers, i.e. bring one drop one, bring both, etc. What is the best way to get them to show what coverage they are in and what are the best routes? I am concerned that our not so intelligent wr's will read the wrong coverages and run the wrong routes. The other team's defense is not very tallented but the scheme alone will slow things down for our blossoming passing game. All immediate help is very much appreciated. Thanks.
Coach Cal