New rotation idea help

I am 5 boxing a tankading + 3 elemental shamans + 1 resto shaman.

For now my resto shaman just sits there casting LHW all the time. Anyways, I was thinking about putting him into better use and let him enter the DPS rotation. The problem is that he tends to run oom much before the elemental guys even get near 75% of their mana pool.

Basically when gryphed + blessing of wisdom + water shield + 4 x mana totems my elemental shamans never run oom even if I am hitting the target dummies during more than 25 minutes nonstop... then I got bored with the elemental guys at near 70% of their mana and thunderstorm unused during all that time.

So my idea was to convert my resto shaman also to elemental and make the following kind of castsequence (simplified for forum purposes)

Shaman 1 --> /castsequence [target=tanks-target] CL, CL, CL, [target=tank] LHW
Shaman 2 --> /castsequence [target=tanks-target] CL, CL, [target=tank] LHW, [target=tanks-target] CL
Shaman 3 --> /castsequence [target=tanks-target] CL, [target=tank] LHW, [target=tanks-target] CL, CL
Shaman 4 --> /castsequence [target=tank] LHW, [target=tanks-target] CL, CL, CL

The idea is that this will overheal the tank because there will be always one shaman casting LHW on him while the others will DPS... and all the shamans will have very similar and predictable mana pool depletion. I have calculated that the overall DPS will be a bit higher than with my current setup because I will be able to put another lava burst into all that rotation combo + another flame shock dot running on the mob all the time.

Also will make my healer shaman a viable toon for PvP rather than a sitting duck complaining that target is out of range or that he is oom.

The problem is... How do I switch the target=tank in the middle of the cast sequence? Is that possible? Has anyone tried a similar rotation before?

So far I have been unable to do that and it's getting me really frustrated.

As far as I'm aware you can't have more than one target set up in a castsequence (and therefore can't switch half way through).

But you might be able to do something similar by using /click (there's a long thread about using this method for stuff like dot rotations, but I can't remember who wrote it), you will need 3 macros for this to work though (and alternative is to have the heal bound to a modifier, but you may have other reasons for not wanting to do that).

So, here's my idea.
The macro on your toons main toolbar (i.e. the button you'll be pressing) has the following info in:

/click <whatever action button the dps castsequence macro is attached to>
/click <whatever action button the healing castsequence macro is attached to>

Then you have the following macros for dps and healing:

(dps macro)
/castsequence [target=tanks-target] CL, CL, CL, ,

(heal macro)
/castsequence [target=tank] , , , LHW

So you have empty commas wherever you want to use a spell from the other targetted castsequence (you may need to add more if you button mash though or use that key for tank abilities). With the empty comma nothing should happen in the first macro for that button press, which should allow the heal in the second macro to get cast.

Editing so this looks more like a helpful post and less like a notebook of scrawled ideas
A much simpler macro for the healing part would be /cast [target=tank] LHW as it won't cast if CL is underway

I think you could even change the first macro to

/click <dps macro action button>
/cast [target=tank] LHW

as theroetically the LHW should not cast until an empty comma comes up in the dps macro.

I would also like to say that this is completely untested, so I apologise if it doesn't work.

You can set it up using /click (link is in my sig).