I have used both Senderos,Song and Gilberto as full backs and it worked out fine. I have also on one occation used Walcott as such, with less luck "ratingwise".
I also tend to use Gallas up front if i need some heading skills there

, and it actually feels like he is doing a good job. He have only scored 7 goals in 5 seasons. But 4 of those goals came when he played up front