The standard way to do it would be to put wrx springs in a Forester strut. The spring mount on fozzy struts is higher up. However the effect will differ depending on your year.
I have an 08 wrx, so it lines up with the 09-11 Forester suspension (for direct bolt on)... with the strut swap I only got maybe .75-1" of lift.
I ended up putting wrx struts back on and instead I machined some spacers (1" in front, 1.5" in the back). Worked great!
I'm still not satisfied, the difference is very noticeable and there's more clearance (about 1.5+ all around) but I think I will go with forester springs and struts for even more.
I did not run into any issues with the swap in terms of clearance, everything bolted right back up. Also, spacers will cost much less and will be easier to install than struts or springs (especially if you make your own, you can do that with basic tools such as a drill and at the very least a jigsaw). I can send you my templates if you want.
By the way do a google search for "The unnoficial how to lift your impreza" thread.