There's no "big secret" to this amazing pattern. You just need a lot of practice and some precision. You can either juggle in on doubles (harder because of the precision needed) or on floaty singles (faster but easier to get down and nicer). Since the siteswap is <3.5p|3.5p>, it's theorically just between a double (4) and a single (3).
J1 starts with 4 clubs (2 in each hand) and make tramline passes (the RH make the first pass), J2 starts half a beat later (with 3 clubs) and throw diagonal passes (the RH make the first pass).
On singles, try to slow down the pattern by throwing higher passes.
7 clubs ultimate : <3.5p | 3.5p>
Reminder : Ultimate = no self
|BN : 64
Sequence : double pass, double self
|BN : 663
Sequence : double pass, double pass, self
|BN : 744
Sequence : triple pass, self, self
If you've understood the BN theory, you'll discover many more patterns using some 5 ball siteswaps.