Sounds like your best bet.
Every other solution I know of means buying new hardware, either a specialized AirPrint server from Lantronix or just getting a new printer with AirPrint built in. Getting your printer onto the wi-fi network is probably the cheaper, even if you have to buy a card for it. Though not a whole lot cheaper. Both the Lantronix XPrintServer and an AirPrint compatible printer can be had for about $100.