Bought mono blocks, now spkr cables too long

Send it to the cable maker and get it chopped up. I did that long ago with some AudioQuest Volcano cable. A 12 foot cable was chopped into four 3 foot lengths. I was even able to sell them later to TMR.com when I no longer needed them.

+1 to the comment by @yyzsantabarbara . The manufacturer is the best one to help you.
In theory, shorter speaker cables are best, because the impedance of the cables influences the sound least. Whether that's audible -- or desirable -- to a given listener in a given system is a different, and entirely subjective, question.

So maybe its a message to those destined for monos. A mono plus is shorter cables.

live and learn.

next he will need longer interconnects.

Yes, i got longer xlr cables.

live and learn