I challenge the rule that is not ok to transplant. chose a time of the day that is not so hot.. evening is best
dig the hole, work the soil at least 2x deeper and wider than the pot itself, so that the roots don't find hard soil to grow into.
Add some straw, wood chips, bark, leaves, compost, even branches of trees, to add air- helps with the transition from pot to ground- right at the bottom of the hole, add more soil, more...make layers of soft materials and dirt. wet it, let is settle, you may have to add more layers.
wet the potted plant, best to soak it inside of another so that its soil is very wet and roots are hydrated fully. gently slide it out of the pot and into the hole. Having it wet, makes the clump come out as one large brick with little disturbance to the roots.
the dirt you remove from the hole - give it some water ahead of time, so it is moist all around but not over watered. put this moist dirt to fill the hole. do not step or try to pack the soil around it, but put it down. if you have more wood chips, cover the entire area with at least 2 inches of chips. to make 'shade' on the area and keep moist in'. you may not water it for a day or two, as there is enough water in the clump for a few days.
That is my method, and it works for me. Even with raspberries that everyone tells me not to plant in the summer. they are doing just fine and keep on growing.
if you don't have bark, find some crimson clover seeds and plant them on the entire area. they grow fast, creating a shade in the area.. and drawing Nitrogen from the air and put it on the ground. Best luck ...
it is best to do all the preparation, weting the soil, hole, and be ready, soon it cools down, you do the rest.