I'm blind - I didn't see it when I originally checked it on WoWWiki. Okay. Lemme think.
Code:
/castsequence reset=7 Stormstrike, Lava Lash, Lava Lash, Stormstrike, Lava Lash, Stormstrike, Lava Lash
The only "pushback" is that the 2nd stormstrike happens on the 9th second, instead of the 8th (due to the GCD caused by the 2nd Lava Lash). Otherwise, it works smoothly.
0.0 - Stormstrike
1.5 - Lava Lash
7.5 - Lava Lash
9.0 - Stormstrike
13.5 - Lava Lash
17.0 - Stormstrike
19.5 - Lava Lash
The cycle starts over starting with a Stormstrike cast on the 25th second. If you're weaving other abilities in there (shocks, etc), there may be more pushback due to GCD's from that. That's why I put in the reset=7 (if it's been more than 7 seconds from the last click, it starts over with Stormstrike).
Another option is to use a much shorter macro like this:
Code:
/castsequence reset=5 Stormstrike, Lava Lash
It's not perfect, but maybe a little closer than the macros suggested earlier (if not as "complete" as the one I did above).
Redacting my first post.