I use this:
Let's you click the button twice for the desired effect. If target is out of range you can simply keep spamming the button till your dots go up. The sequence will reset to the first step after 5 seconds OR if you switch target. So you can put up SB:SS on mulitple targets, really, really fast. Upside is also that you won't need a seperate button for Soulburn, most likely. Downside is that if you target switch after pressing Soulburn you use a second shard.
#showtooltip: Soul Swap
/castsequence reset=5/target Soulburn, Soul Swap
Hope this helps.