it takes a little time but well worth it. I have done it to my ej9. however I had Vti rear seats, basically the same as yours. not too hard but there are some sharp edges.
1st - The bottom part of the seat (the foam you sit on should bolt straight in)
2nd - Because the mounts are different on the ek9 back support part of the seat, your going to have to sacrifice your ek4/sir ones in order for them to fit. Both seats have a metal frame at the back of them. you will need to remove the seat cover and foam from both sets of the seats.
3rd - You then take the vti/ek4 METAL part of the seat and insert them into the ek9 foam (make sure you put the right metal part back in, it should have bolt holes where it should be mounted, not a bar!)
4th - Simple case of putting the metal clips back after making sure the fabric is firmly stretched back.
5th- should be able to bolt straight in.
Hope that answered you question. =]