This is a classic "mistake" that I've made many times when going for The Oracle, especially, or The Great Wall.
There are two ways around it :
- you can gamble on a low odds Scientist in your wonder city ;
- you can set up a Library in city 2/3.
Here, Memphis seems pretty well suited to pop the first Great Person.
You "just" need the Library up and running more than 17 turns before the GP would be born in the GW city.
It may mean going for Writing before BW, depending on the early tech path.
Egypt being Egypt, here, you can either use an Obelisk on top of the Library, if ever the race is too tight.
Of course, there's a drawback to the early scientist : you're losing on production, about 100 food/hammers, or the cost of a settler (plus the incidental commerce).
Depending on the land, it may be better to forego the early scientist and grab strong cities.
If you don't want to lose too much food/hammers, then gambling on a low odds scientist is the way to go.
Not saying this is the way to go but even this would work :