Binary data, matlab function block

I have a problem with simulink, i have a certain binary data (bernoully binary) then i add redundancy at the begenning, i add 8 bits (1) a mean, 11111111 before the random binary data (message), i have to make the program recongnize de 8 ones (1111111) and then start reading the message after de 8 ones, it is like a RUN BIT, i need this because in my simulation many blocks create delay so I add the 8 bits in the message to tell the simulation to star reading after those 8 bits, i tried to do it with matlab function block, or any other way but i couldn't do it, i need help.