First, let me make sure I understand your question:

You have accountA (70 druid on comp1) and accountB (60paladin on comp2). You want to powerlevel the paladin and also use the him/her as a buff & heal bot. Correct? Furthermore, you want to pass "actions" to accountB via mouse clicks instead of keystrokes. Correct?

Couple of questions: how many keyclone licenses did you purchase? You would need two if you use Keyclone (one for each computer obviously).

Keyclone can indeed pass mouse clicks. See this thread for starters.

HotKeyNet can also pass mouse clicks. See this thread for startes.

Basically, you need to pass a keystroke string via mouse click to accountB on comp2. So "leftmouse" would be translated to "1" for example on accountB, comp2. On accountB, comp2 you would place a macro on actionbar 1, slot 1 (the default keybinding is "1"). That macro would be some variation of:

/target party1
/cast Flash of Light

For the /target piece you can target by name, party, focus, etc. Whatever works for your setup.

Hope that helps you get started. Reply back if you have further questions or need clarification.