There are a lot of things to consider besides seaming if you convert a pattern from dpns to straight needles. When you go from working in the round to working flat, you will need to figure out how to work your WS rows. For example, if the pattern calls for st st, working in the round will require you to knit each row while working flat will mean working a knit row, then a purl row. Also, when working in the round, your pattern will give directions for each row going from right to left. Converting to flat will require you to reverse those directions. For example, if the pattern reads "k2, p3, k4, p5", you will have to reverse that to "k5, p4, k3, p2". And how do you do your WS decreases/increases so they lean in the right direction to fit into the pattern?
People who are comfortable working with graphs might be able to chart a pattern so you can knit flat instead of in the round, but otherwise, I don't think I would attempt it. But then, that's just me! :aww: