Try this link-
www.bassplayer.com/z1998/9809/larue.shtml
Larue's exercises incorporate BOTH hands into the slap/pop equation. IMO, that's a direction you'd want to explore.
Slowing Larue's pattern down abit(his examples are in either 1/8th note or 1/16th note grooves).
T=Thumb
X=Fretting Hand Slap
P=Pop
Count 1-2-3-4
Play T-X-T-P
You can practice this "pattern" with the strings muted...
THUMB the OPEN "E"
SLAP the strings agianst the neck w/ fretting hand
THUMB the OPEN "E"
POP the muted OPEN "G"
So, it's
Thumb-Slap-Thumb-Pop
Later, you can mix it up-
Thumb-Pop-Thumb-Slap Thumb-Thumb-Pop-Slap
Etc...
Another exercise-
1)Mute the strings with your fretting hand
2)Play a consistent & even Thumb-Pop-Thumb-Pop(1-2-3-4). Once that's comfortable, you can begin eliminating certain Thumbs/Pops as YOU hear fit.
IMO, this concept is used on a tune like "Aeroplane".