Boot using partitioned USB flash

[sambat]

I partitioned a Sandisk Extreme flash drive and have been trying to figure a way to place an iso boot image on the first partition (leaving the second empty for now).
The programs I normally use to write an iso to usb (UltraISO, Rufus) insist on wiping both partitions before proceeding.
Anyone know if it's possible.

[sambat]

Found a solution.
Wrote the iso file to the drive then ran a program called Partition Assistant and split the single partition into two.
Assigned a drive letter to part 2 and wrote files to it.
Booted using part 1 and was able to read the data on the second part ok.