You actually can prevent immediate downloads following checkout, requiring the buyer to obtain a link to their download page from the thank-you email we send them.
In Seller Admin > Edit Preferences, enter a Common Thank-you Page URL; all of your buyers will be directed to this page following checkout, regardless of which item(s) they ordered from you, bypassing the standard thank-you/download page we'd normally generate following payment. On that same screen, remove the [%thankyou_link%] template tag from your Common Thank-you Email template, or you can just disable that message entirely; that tag inserts a link which (in this case) would just redirect to your Common Thank-you Page URL, so there's little point providing that in an email.
In the settings of each product, make sure you leave the Product Thank-you Email message enabled. If you also choose to Enable Templated Email, make sure your custom Email Message template includes the tag [%download_link%] where you want us to insert a link to the buyer's thank-you/download page for that item; however, if you do not tick the box for templated email, any custom Email Message you enter would be inserted after our standard greeting and link presentation.