I just did it mostly manually, using roughly the following steps:
Load the main xib window into Interface Builder, use the IB Create iPad Version menu to convert it to the iPad version and save it under the corresponding name (suffix "-iPad.xib" is common).
In Xcode, add this new .xib file to your project and include it in the target.
Modify the Info.plist application to name this new ipad xib under the key "NSMainNibFile ~ ipad".
Change the build setting to say iPhone / iPad as the target device.
Add code checks at runtime, for example:
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) { ... }
to handle any programmatically created user interfaces or drawing differences, select iPhone vs iPad xib, etc.
Add appropriate icon sizes, default images, etc.
Redesign your views to further display more things, autoresist to support more turns, use popovers, etc.
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