Adrian Carter, you first asked the question in August 1997, and today you get an answer.
Clive Robertson did indeed play SPRECHEN SIE DEUTSCH by THE NAFF on his ABC radio programme.
After playing the record (yes, I still have the single), to the best of my reckoning these are the lyrics:

If you want people to like you, learn German
If you want love and affection, whisper "ja, ja"
If you want people to say "howdy doody"
Change your name to Dieter or Rudi
Give them something to think about
Stand up straight, talk in kraut
"Danke schon, bitte schon, ja, ja, ja"

If you want people to like you, learn German
You'll make so many friends when you SPRECHEN SIE DEUTSCH
'cause smiles break out at the sound of kraut
When a german voice is heard (achtung)
'cause today it's a frankfurter sausage, tomorrow the world

Oh, if you want people to like you, learn German
Wear a monocle and a jewelled(?)spur(?) (all the way from Heidelberg)
And if you want that popularity
Try to speak your Deutsch with clarity
Swig that beer, drink that wine
Make the trains all run on time (toot, toot)

If you want people to like you, learn German
You'll make so many friends when you SPRECHEN SIE DEUTSCH
So act real merry, sing in Gerry
And chat up all the girls (hello Schatze)
Because today it's a frankfurter sausage, tomorrow the world

(music)

Then you'll come back from Paraguay
(but next time no more Mr. Nice Guy)
Drive around in a big Mercedes
Enjoy interrogating terrified ladies (You vill answer ze qvestion)

If you want people to like you, learn German (whoa)
You'll make so many friends when you SPRECHEN SIE DEUTSCH
So have some fun, talk in Hun
When the German flags unfurl (ticketty poo)
'cause today it's a frankfurter sausage, tomorrow the world.

Oh, if you want people to like you, learn German
Girls will let you kiss them upon the neck (you're djoking)
Germany will become a power again
If you annex Czechoslavakia
Fly Stuka (?), drive tank
Put your Deutschmarks in the bank

If you want people's love and admiration
Then try to assimilate them two-ton traits (that's what the people like)
So shine your boots up, brush up your goose-step
Get them Panzers oiled
Because today it's a frankfurter sausage, tomorrow (x3)
There's so much love you really can't knock it
For the guys who invented the B2 rocket
Today it's a frankfurter sausage, tomorrow (x3)
If you're going to London today
Fly Lufthansa (ve know ze vay)
Today it's a frankfurter sausage, tomorrow the world (vody-o-doe)

That should satisfy those who couldn't quite remember the song.
It was a good one.