Well I did the same conversion on my 2002 748R and took pillions with no trouble and I'm not as light as I'd like to be
Something you do need to consider though is telling you insurance company, being an R and single seat you won't be covered to take pillions
Much better off keeping you R for yourself and buying a M600 for her to ride on her own and you can go racing on it at the weekends
Darren