You don't have to lie on your back to do a WILD. Choose the position you're most comfortable in. I always lucid dream on either my side or on my stomach. If you haven't, I suggest you read some tutorials in the Wiki: Wiki - Dreamviews Lucid Dreaming Community & Resource

I personally haven't done much WILD as I get too excited. I rely on the MILD and DILD techniques to get lucid.

Good luck! If you have any more questions, feel free to ask them here or PM me or any of the other Dream Guides.

Keep on dreaming!