Sounds like a nursery pot tree...They do back bud on old wood...but, remember...it doesn't hurt to hold out for better material. Not all trees need to be bonsai. Is there any taper in the section that is straight? You mention pole...You will be spending a long time creating something from nothing. I just pruned mine back mid June because I seen Jonas on Bonsai Tonight doing it on a blog earlier than July, because of strength. Mine was strong and taking over the section of landing it was sitting on. So I pruned back hard...and this is how it's recovered from that hard pruning.
I will say, many say they hide their wisteria during the year out of bloom. I don't do that. I embrace it. It sits here on the landing where it can grow wild...and not be in the way of anything. But now, it's lovely! It greets guests as they visit. (Of course we are on covid no one in the house. But we have had neighbors visit 6 ft. away. This one was just admired the other day by guests...the trunk line pulled them in. ) *Sitting in a commissioned Sonny Boggs pot.
A few of his blogs may be helpful...
Cutting into old wood on wisteria bonsai to create a more compact silhouette.
bonsaitonight.com
This was why I trimmed mine back earlier this year...
Photos showing spring cutback and leaf pruning on a Chinese wisteria.
bonsaitonight.com
As you see mine was growing quite strong...
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Hard prune back to how he explained of the compound leaves. (That really was a first that I have done to that extreme...and it rewarded me.)
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