Cast on enough sts that's a multiple of 4. Make the base triangles like you do for an 8 st multiple (or 10 or 6) only do it as far as 4 sts, then start the next triangle.
I will say that by the time you pick up sts on both edges you're only going to have 2, maybe 3 sts in your squares and triangles, so they're pretty bitty. Maybe try a 6 st one instead. Here's a tutorial for a 6 st scarf, that might help.