Ways to increase effective cleric level for rebuking undead on a multiclass cleric?

[Socksy]

I have a boss fight I'm going to throw at the players. It's a multiclass Cleric 11/Entropomancer 10, but they ran into it early and so I grabbed the generic High Priest stats from DMG2. And it successfully Rebuked the party's lich into running away very quickly.

I want to be consistent though, and looking at it, it won't stand a chance of turning the Lich as things currently stand.
I'd rather not use homebrew if I can avoid it, and please don't say "You're the GM, you can give it any abilities you want!" because that isn't how this particular group plays. Feats and classes available to enemies are also available to PCs.

Is there a feat like Practised Spellcaster for rebuking?

[danielxcutter]

Well, there is the Improved Turning feat, but that one sucks.

This (http://webcache.googleusercontent.com/search?q=cache:OTymGDGlg6YJ:www.minmaxboards.com/index.php%3Ftopic%3D2733.0+&cd=1&hl=en&ct=clnk&gl=us) handbook does have some tips, though.

[Anthrowhale]

Heighten Turning/Empower Turning are the obvious feats.

[GilesTheCleric]

What resources are you looking at using? There's items, feats, spells, and prestige classes.

[Socksy]

Any non-homebrew resources I can access online or through rulebooks, of which I have many and am always willing to add to my collection.