Pathfinder does not directly support Epic or 10th level slots which is hard-coded into an array.
If I was to do this I would need to think outside the box and use many of the flexible pieces of HL to achieve this. A Configurable is capable now of supporting a list of spells. So you could write a custom script on the Configurable to change the Custom Expression for its spell selection. I would change it to the following in example:
Code:
component.BaseSpell & Custom.EpicSpell
Then I would make my "Epic" spells and set the new custom tag of "Custom.EpicSpell" on these Epic Spells and set the spell to no class or level.
So then you would have a Configurable tab (Maybe set to a Mechanic) that would allow selecting these special "Epic" spells. You may run into other issues with metamagic and stuff which you would have to work through. You may need other logic and scripts to set uses per day and stuff. But at least you would have a special tab that could add the spells to your character.
That would be how I go about it. And if everything above I just said sounds like Greek to you then I would say this would be a awful first project to learn the HL editor. When you are trying to make HL do things outside its normal behavior you first need a very good understanding of its basic building blocks.