A SCART connection can be used as both an input and an output. But what you are trying to do in this case, unfortunately I feel it is not possible.
Typically STBs are designed with outputs only at the back, with the exception of an input for the antenna signal. Such is going to be the case with your Topfield PVR, no matter what adaptors you use.
Try to find some way to directly connect the Wii to the TV. Extension cables maybe? Sorry if thats lame, but not familiar with your setup.