2005 Prius w/Nav and JBL - Want Spotify on iPhone

I searched and couldn't find this specifically. So my wife has a birthday coming up and I wanted to get her something to integrate her iPhone. We have an '05 with Nav/JBL/6-disk changer in dash. No aux input in console. I think most of the iPhone devices utilize either CD emulation or Mini Disk (MD) emulation.

I know there is the DICE units, GROM, Viastech, and a Peripheral devices.

With my 2005 hardware, is there any unit that someone has identified that will work to either:

1. Display something on the screen that emulates the spotify interface (much like the MediaLinQ Plus does for Pandora - that I don't think will work with my hardware)

2. Allow the steering wheel controls to control skipping tracks, at a minimum.

She has an iPhone 4, and will prob. get an iPhone 4s at some point in the future, and is running latest iOS version.

With the growth of spotify, I'm really hoping that someone has run into this desire. I really, really, really, wish we had just found a 2006 or newer so I wouldn't have to be limited by the hardware here, but alas - it was a great deal on a great car.

Lastly, if the delta between the pricing is something like hundreds of dollars between just getting a hard line connection to the head unit (still control everything via iphone) and rudimentary integration (being able to skip tracks via steering wheel) then it may not be worth it to me. In that case, what is the best, cheapest option here, just to have a hard connection?

My thinking is that she will really only use spotify, but possibly pandora. I don't even think she has any actual music on her phone and don't know if she ever will, so I don't really think the playlist/disk emulation the current solutions offer would be of any benefit.

Looking for comments/suggestions! Thanks!