Doesn't Online offer a vendor report where you can select "Print on Check as"?

Create a report that has Vendor and this field, export to excel, save it on a sheet, then export your transaction list of checks, do a vlookup on the vendor to the other tab and return the "print on check as" field and build your export from there.

I do this in desktop, not sure if it can be done in Online, but I would figure similar functionality.  This is how I'm building the check positive pay file for our bank.  Or then again, pay for the guy aboves product to do it for you automatically. 

Travis