Here's my advice (assuming that you want vacant possession as soon as possible):

1) Don't waste time and money to enter into an agreement with him;
2) Immediately appoint a lawyer and instruct your lawyer to serve him an eviction notice;
3) Obviously he will ignore as he will stay there until Feb 2011;
4) Instruct your lawyer to file an application to obtain a court order to compel the occupant to vacate the premises;
5) It will take around 2 months at the earliest (very rough estimate) for the lawyer to obtain a hearing date, get the order before the Judge, file the draft order, extract it and file the faired order, and extract the sealed order.
6) Once all that has been done, wait and see if the occupant has vacated the premises or otherwise. If he has not (which he most probably will), then instruct your lawyer to file a distress application in Court - the Court bailiff will escort your lawyer (you may be present as well) and compel the occupant to vacate the premises. The occupant will definitely surrender vacant posession to you by this time.

If you do enter into an agreement as you said, you would have to wait until Feb 2011 to see if he vacates the premises or otherwise. If he doesn't, you have to start steps 2-6 from Feb 2011, and by the time all is done, another few more months would've lapsed.

It all depends as to how fast you want vacant possession. If you don't mind waiting, just wait until Feb 2011 until you start step 2 above. Essentially, any agreement which you enter with him now would not have any basis or relevance come Feb 2011, because you are still obliged to serve him with an eviction notice.

PS: If you want to find out about other purchasers who have bought properties under auction and experienced a similar predicament, may I humbly suggest that you open your own thread in the forum and ask there.