Likewise, I have no idea what the EP trick is.
But, two thoughts. First, buy a first season from Monday in Week 1 to Friday in Week 5, and the second from Monday in Week 6 to Friday in Week 10. That way, all travel will be at monthly rates, and the number of non-travelling days paid for will be minimised (I assume that there is no need for a ticket for the weekend between Weeks 5 and 6).
Second, I note that season tickets from Hillside to Burscough Junction (via Southport and with a walk from Burscough Bridge to Burscough Junction) are cheaper than season tickets from Hillside to Burscough Bridge (£112.60 for a monthly instead of £124.50). And a Hillside to Ormskirk monthly is also £112.60, and seems to be valid via Burscough or via Sandhills (i.e. the National Rail Enquiries website offers both routes for the £6.50 anytime day return from Sandhills to Ormskirk). I assume this is because the only Hillside-Ormskirk return is the £6.50 anytime day return, whereas there are anytime day returns and offpeak day returns between Hillside and Burscough Bridge. Indeed, if all Monday to Friday travel will be after 0929, buying a £4.80 Hillside to Burscough Bridge offpeak day return each day may prove marginally cheaper.