There are a couple of types of regulator - one for the disposable bottles and one for the bigger refillable cylinder.
If the welder has a dispsosable bottle regulator you could just plug a disposable bottle in (very expensive way of doing things) or otherwise buy an adapter and a cylinder regulator (cheap enough) and hire a gas cylinder. Only other thing needed to change to gas after gasless is a change of wire and a change of polarity (terminals unscrew inside the welder).