[NTG-context] substituting characters in math font

I need to substitute the regular and italic characters of a publisher’s non-math font (Unicode) for those in a math font. The non-math addresses are: 0041-005A, 0061-007A %italic uppercase and lowercase 0391-03A9, 03B1-03C9 %slanted Greek uppercase and lowercase The math addresses are: 1D434-1D44D, 1D44E-1D467 %italic uppercase and lowercase 1D6E2-1D6FA, 1D6FC-1D714 %slanted Greek uppercase and lowercase Is there a way to use the \definefallbackfamily mechanism that does not assume that the characters have the same Unicode addresses? Or is some other approach required? Alan