You can configure DWP to send E-Mails for the approval requests to the managers - the user has to choose to configure this in their DWP-Profile under preferences:
If you set E-Mail to true under Approvals, they will receive E-Mails when approval is required. They do then have to click on the link in the E-Mail to open DWP and approve (or reject) the E-Mail.
Thanks for your input.
We will try this and let you know the result.