I think you're probably right about the absence of a suitable cable. The adaptor isn't cheap, but my mate will have to balance the respective costs of the cheaper HDMI reliant flat screen and dearer, more flexible products.
The freeview channel selected will only be output via the RF out link if the freeview box has an in-built RF modulator. Early models had a modulator but later ones do not. It is possible to purchase a modulator or use can be made of a VCR, feeding the freeview Scart output into the VCR and using the RF modulator in the VCR, used to provide an RF output for tape recordings, to connect to the TV via the RF out connector.