No, there isn't. fit and fittype need to know the number and names of the unknown coefficients, and the only way they can do that is to have them listed as individual input arguments in the function signature.
For the problem you've shown, however, you would never use fit(). The model is linear in the unknown parameters and can therefore be solved algebraically as below.
z=[5.26;7.58;12.64;15.38;12.64;7.58;5.26];
x=linspace(-pi/2,pi/2,7)';
q=2;
G = [x.^0, cos(x*q), sin(x*q), cos(2*q*x), sin(2*q*x)]; % this is fourier2
p=G\z
