The Discrete Filter block under Simulink/Discrete should support your needs. You'll just need to simplify numerator and denominator to [a b c ... ] form, where a is the constant coefficient in the polynomial series, b is the 
coefficient, etc.
coefficient, etc.So, for instance,
would enter as:
numerator -- [1 -1 2]
denominator -- [1 1]
(Note that I suggest the Discrete Filter rather than the Discrete Transfer Fcn because the Discrete Filter expects negative z coefficients, with the first term always being 
, whereas the Discrete Transfer Fcn expects positive z coefficients, with the last term always being 
.)
, whereas the Discrete Transfer Fcn expects positive z coefficients, with the last term always being .)
