Furigana is supported by several localized products. TurboWriter, EGWord, and Nisus support Rubi/Furigana, and we believe that MacWrite II-J, WordPerfect-J, PageMaker-J, Quark Express-J, and others, may support this feature.
We feel that simulating Furigana by adding an extra line above your line of text is a poor solution because the Furigana needs to be anchored to its associated text.
For additional details on third party Japanese Language Kit products, contact a Japanese Language Kit dealer in your area, or contact a third party software vendor, such as, SystemSoft.
The Tech Info Library article titled "Locating Vendor Information" can help you search for a particular vendor's address and phone number.