Here are some partial solutions:
If you were willing to change your PP to Traveler's Harlequin, you could dip into bard for Combat virtuoso.
As a half-elf cleric, I assume that you've gone for ranger because of twin-shot, and your paragon of victory certainly supports that assumption. I assume you're using a greatbow for 6.5 average damage per shot with one feat.
If you go invoker instead, with the feat silvery glow, You get 1d4+wis+2. Given that your wis is almost certainly 20, That's average damage of 9.5 on three targets. You do give up single-target focus fire, however. And while there are no "pour on the pain" encounters or dailies for invoker quite like there are for ranger, there are plenty of excellent ones. This also puts you in an excellent position to take Morninglord which should output more damage than Path to victory.
There is the obvious solution of being a bard, of course.
Then there's druid. Druids have Magic Stones (which are 1d4+wis push 1 an they're untyped, so changing them to radiant or cold or what have you is easy enough). As their level 7, they have a dominate with Charm Beast (dominates anyone, more accurate on animals) which provides significantly more damage than a double-attack. (consider having your "charmed" minion charge one of its allies right past all of your melee combatants. While multiple 3[W] attacks are hard to argue with for a daily, I suspect a large summoned croc would give them some excellent competition.
However. In my experience, when I've played for optimized-for-at-will characters, you don't want encounters and dailies taking up that all-important twang-twang. The bard's prescient warning is astonishingly good as are a great deal of warlord powers. Ignoring the fact that at-will spam characters have been very very boring for me to play after the first few sessions of being awesome, your best bet is warlord/ranger or cleric/druid.
At the end of the day though, your approach is a bit off. As a leader, you should be wielding your party members for their greater damage. You can help them optimise for damage, and then you can enable them to do far more damage than you could do otherwise. Being a leader who wants to be a solo striker, I have found, either means that you should be honest and play a damage-dealing striker/defender/controller or use your party members as your implements. If you really must continue in this path, take a look at the Frostbow of Sehanine which uses his/her encounters and dailies to buff twin-strike.