Most advanced arrangers can be configured to produce a bass note and a lower pad (strings, choir) sound in the left hand, even if they don't have dedicated panel buttons for doing this.
The key is revoicing the style with a bass voice that is monophonic, so that when you play chords only one bass note (the root) is heard. Choose a pad sound like Strings or Choir with a long attack and release.
You have to trick the accompaniment by activating "sync stop", so that the pattern doesn't continue when you release the keys on the left side. Each time you press the keys, the accompaniment pattern will restart at measure 1 beat 1, sounding the root bass. Eventually the strings/choir will come in.
The other trick is to mute all of the style channels EXCEPT the bass and whichever channel contains the pad chords. On Yamahas this is usually channel 14, sometimes it's even called "Pad." The result of all these changes will produce an accordion-like effect. When you need to use the arranger function again, turn on all of the style channels, and release the sync stop.
I agree with Rogsza, the Pa5X is very new; I personally wouldn't consider it until more of the features are implemented and working. Please let us know whether my idea worked for you, and what you decided.