ELW I'd like to try that sauce although Kraft Miracle Whip sounds like one of those hard to get American imports. 
Gav Please PM me the damage for the shatkora pickle. 
MushroomMike,
Miracle whip is available online, but just double up on the normal mayo instead.
**give the sauce a blast in the microwave for about 30 secs than cool & refrigerate**
The dill relish / sweet relish (to give the sweet & sourness) can be found in Polish supermarkets or the Polish section of a uk supermarket. Try there for jarred stuff (Vlasic brand does both)
If you don't have dried onion, at least soak the fresh chopped in water for as long as you can.
Fresh onion will ruin this little project, as will supermarket burger buns, which are nowhere near as sweet.
Tips for closer authenticity: Assemble upside down in under 10 seconds, leave lying for around for 45 mins, serve and enjoy

Regards
ELW