Update @ 2009-05-30: The information in this post is incorrect, the no ip next-hop-self eigrp command changes EIGRP next hop processing.
Yap Chin Hoong sent me a detailed e-mail describing his efforts to use the Next Hop field present in EIGRP routing updates. His conclusions (that I’ve subsequently verified with a few lab tests) were disappointing: although EIGRP updates have a next hop field, it’s not used (unlike OSPF forwarding address).
When doing the tests, I’ve reused an old NBMA topology and thus started to wonder whether I hadn’t already tested the EIGRP behavior. Turns out I had … and summarized the EIGRP behavior as “EIGRP updates contain no provision for changing IP next-hop address” in the Next-hop fixup in partially-meshed NBMA networks article (In the meantime, I’ve fixed the text to reflect the reality).