I understand that you have created a spline using 'cftool' and would like to use the same in 'splinetool'. You can do so by taking a function handle and use it in 'splinetool' An example follows: You can construct a cubic spline interpolant that matches the cosine function at the following sites x, using the csapi command.
x = 2*pi*[0 1 .1:.2:.9];
y = cos(x);
cs = csapi(x,y);
You can then view the interpolating spline by using fnplt and get its handle-
Now, you can use 'h' in 'splinetool' when it prompts you to import your own data.
Hope this helps!