Have you tried:

Code:
/cast [target=focustargettarget,help,nodead,exists] [target=target,help,nodead,exists] [target=player] Lesser Healing Wave
I think you can remove "exists" as well as checking "help" already implies that the target exists.

EDIT: See http://www.wowwiki.com/Useful_macros....28Friendly.29

EDIT2: Also from WoWWiki

exists
This determines whether the given unit exists. In other words, if you don't have a target, [exists] will return false. If you have a focus, [target=focus, exists] would be true. Note that in some cases [exists] is unnecessary. [help], [harm], [dead], [party], & [raid] all imply [exists] if they're true.