Sure you can practice without the actual approach,
from medium alt:
reduce throttle and drop the nose some to get a glide slope
start your slip
keep it stable in glide & heading for 5 or 6 seconds
now get out of the slip & start a slip in the other direction

You can practice this reversing the slip controls till you can keep the plane stable in its glide slope... wherever that glide may be: up 2 mistakes high or on final 20' up. Just remeber that the slip is a drag monster, and you will lose speed- watch out for stalling! But practicing at high speed doesnt give you the right feel for the rudder at landing speeds, so practice slow, but HIGH UP. Will also help get the feel for the slipping stall speed & corrective actions... something not availible when practicing low, where corective action involves CA, Sticks, & Ironing

Even if you cant see the plane 'slipping', you know it must be from the TX being max Rudder & some Aileron, but the plane is going straight on the slope.