shader evaluation on specific frame

[nospitters]

hi,

i want to write a shader for xsi that renders lets say frame 1, 1.25, 1.5, 1.75, 2 then puts all these "subframes" together to the image.
but dont know where to start.
how can i tell the shader to render frame 10 instead of the current frame?
tried with CTime time(10), but no success. also with time.PutTime(10)...
any hints?

c++, xsi, mental ray