Can you get a spreader pole with a spike each end?
That'll do to hold the main part.
Use shock cord as a small loop to go under hoop and back on the spike.
Spreader pole is anchored to the hoops.
Measure up the distance between the foot end and the middle loop.
Measure your tent poles and when you find the one that's longer in the spike end.
Flatten the end and make it into a U shape. So the U drops onto the hoop.
The U shape sits over the hoop and held in place by shock cord.
The spike end fits to the middle loop just like your first pole down the middle line of the swag top.
That'd do it, I reckon.
There must be lot's of other ways.