In practice, under VFR, ATC pass the recommended vortex wake spacing to the following pilot. It's up to him to make whatever separation he requires.
Downwash, by definition, flows downwards. As long as you can see the preceding aircraft it's no problem to arrange a steeper approach if required, to keep above its wake. Downwash also drifts with the wind, so lateral spacing from the wake can often also be achieved when approaching the runway.
If this isn't possible then it's sensible to keep to the recommended spacing distance.