During the last blues class we did a 12-bar blues by stringing together riff #1 and riff #2 . We did this in the key of G by doing 1st measure as riff#1 in G , 2nd measure riff #2 in G, 3rd measure riff #1 in G, 4th measure riff #2 in G..........................Then 5th measure riff#1 in C, 6th measure riff#2 in C.....................7th measure riff#1 in G, 8th measure riff#2 in G.......................then 9th measure is riff#1 in D, 10th measure is riff#1 in C, ............... 11th measure back to riff#1 in G, ..............and the 12th measure was a quick turnaround (such as a 4 - 5b - 5) which brings you back to the beginning.. Sounds good if you can do it smoothly (takes plenty of practice).