You could but pilots get paid alot more then FA's so most of them would not like to. Also a pilots and Fa's job you could go at any time so you will have to work out that. I think most of them would not want to though. Also hours might be a problem.
There are some planes were you are pilots and FA's like British Norman Island.
It could be done but would be alot of work and I do not think it would be really worth it. If you want to be both be a FA while you are doing you pilot training then become a pilot.