one (quite complex) solution could be using the ftl approach (if you are using keyclone)
for this see: http://www.dual-boxing.com/wiki/inde...aderless_Setup

another approach would be (if you are using a tool to get macros above 255 chars), using a assist/cast-macro like:

Code:
/assist [target=ToonA,nodead][target=ToonB,nodead][target=ToonC,nodead][target=ToonD,nodead][target=ToonE,nodead]
/cast Lightning Bolt
The last approach would be using the focus to define which is aour master and bind keys to switch your focus to another toon in combination with:
Code:
/cast [target=focus-target,harm,nodead] Lightning Bolt
in combination with jamba, you could use zanthors approach (which looks realy great and much simpler than the ftl)
see: Leaderless/Targetless - Focus Based Hydra