Idiot-Proofing Soul Swap

[Retrofire]

I'm trying to idiot-proof my Soul Swap macro for raiding. The current problem is summed up thusly:

Typically in a raid situation where we have multiple targets up, I'll try to Soulburn + Soul Swap DoTs onto several targets as long as I have shards to support it.

The problem arises in the following circumstance - If either A) I am out of shards and haven't noticed, or B) my alt key is not completely held down, the Soulburn will not fire, and the net result is soul swap will inhale the DoTs off my target rather than exhaling to refresh them. This can cause a huge DPS loss, because, this is most often used during Dark Soul while I'm burning the boss or during the execute phase, and rather than refreshing my DoTs as desired, I actually end up pulling the DoTs off my target, and to make matters worse, I can't simply eat the lost GCD, and re-DoT my target, I have to manually replace all of those DoTs. The cost of this error in DPS is absolutely brutal.

TL;DR version:

1. Attempting to Soulburn + Soulswap to refresh DoTs on target
2. Either insufficient shards available or fat-fingered ALT condition on macro
3. Result is sucking the DoTs off the target and having no quick way to reverse the error. Forced to refresh DoTs individually and resume execute rotation.

What I'm using now:

/cast [alt:mod] Soulburn
/cast [@mouseover,harm,exists] Soul Swap; Soul Swap

What I want:

Macro will only attempt to cast Soul Swap: Exhale, and simply won't work if the Soulburn condition is not met. Is it possible to cast Soul Swap: Exhale via macro, rather than the generic Soul Swap, which has the potential to bone you if you mess up the Soulburn (either through failing to notice insufficient shards, or ALT key malfunction/fat finger?)

Thanks in advance for any help here.