You can buy adapters or PTO parts and convert it to "work", but it aint gonna mow well at all. Running at half its rated speed will make for some VERY slow mowing in heavier stuff. I am sure you will be dissappointed.
Depends on how cheap it is and how much work you want to do, you could also put a 540RPM gear box on it, but they cost $100-$200 for just a cheap one.
And you didnt mention where you are located, but if it is anything like where I live, Bushhogs sell cheap ALL the time on c-list. I'd check that out and wait till the right one comes along.