Hmm yea, in Baan IVc4 you can't really sort on anything other than the main table index.
How are you linking table B to table A? Would it not have the same index as A, since you have a 1 to 1 relationship it seems like? (Maybe an example with your table indexes and relationship would help if I am mis understanding that). One suggestion, can you just make the main table B instead? And change all the view fields on the form to B instead of A. You can then use the sort from B....I may be missing or assuming critical issues, show us your table structures.. You could update table A based on updates to Table B if you need this to be a maintain...that could get messy as well, but it sounds like you just want the display.
Or..make a report that sorts like that and add a button to print it.