Could always just cover it with one of the molle system seat back storage units (most go across the front as well though - search them on Amazon to get an idea). Otherwise, try an Auto upholstery shop - they may just pull the entire seat cover off to fix it.
FWIW I HATE when people damage by shyte and make no offer to repair in on their dime OR offer no apology---learn a lot about people (no matter who they are) when it comes to doing the right and honorable thing.
Such an incident tends to be the last time I loan them ANY thing!
Not a fix but I agree with TwoXentrix. I installed the below product. It does not exactly fit. it took a bit of getting it into place. But I am happy with it. It adds extra storage and looks pretty nice. I you want I can send photos later. Just let me know.