AOG - I think he could frame his apology along the lines of - "Although there is no evidence to support any claims that I acted in an illegal fashion towards any of the ladies involved, if i have caused any distress, up to and including their requirement to give evidence to the Disciplinary Panel, then i would like to apologise unreseredly for any part I may have played in creating that scenario."
That doesn't admit to any guilt, but it does chime with the concensus that there has been inappropriate behaviour, but not enough to secure a criminal convction.
Saying sorry doesn't take ten years off someone's life - it would be a more dignified end than the political (ly correct?) corner that Nick Clegg has painted himself into - unseemly squabbling about being asked to apologise, and being told no, helps no-one.