What about those procedures I found on the Internet, such as soaking wormwood in vodka, or dosing Pernod with wormwood extract?
All of them were created by people utterly ignorant of how to create absinthe.
Absinthe is a distilled product. You CANNOT make something approximating absinthe without distillation. Soaking barley in vodka won't give you whisky. Soaking wormwood in Everclear won't give you absinthe. It won’t taste like absinthe, and it won’t BE absinthe. All you’ll have done is turn a perfectly good bottle of neutral high proof alcohol into a disgustingly bitter, vile tasting mess.
Pastis isn’t absinthe without the wormwood. Adding wormwood essence to pastis won’t make it taste like absinthe. Undiluted wormwood oil is also a potentially dangerous substance, and can lead to severe renal failure if drunk neat. Stay away from it.
In short, unless you have access to a still, it is not physically or chemically possible to make anything remotely approximating absinthe.