Hmm, $1500 bounty and performance reviews tied to patents. I suspect you were working for a big company which made you blue to the point where you had to leave.
If it is who I think it is then, yes, your employment contract will detail that all work carried out by yourself during your employment is owned by the company (as do all their contracts, I believe). Even if it's a different company, the fact that they submit patents at all probably means that their employment contracts come with similar clauses. IP is very important to many large companies.
In employment contracts I've seen, they've even tried to claim stuff that was unrelated to the work that people were doing for them, but people have gotten that stricken before accepting, since they may have been doing contract work or their own stuff in addition to what they was doing for the company.
So, bottom line, they almost certainly own the work you did before leaving, including that patent submission. Hence, no, you cannot stop this patent from being filed since you have no control over that.
What you can do (if you feel strongly about it) is to try and stop it from getting to the NOA (notice of allowance, meaning that the patent has been approved) stage within the USPTO.
First, I would cash the cheque. $250 is $250. It's not a reward for supporting the patent. It's really just the company trying to stop you from causing them trouble and, unless it's attached with an official agreement for you not to oppose, you can take the money and run.
Then I would notify (in writing) the lawyers of the prior art and why you think it invalidates the submission. They will then be legally required to bring that information to the USPTO as part of the submission. However, these lawyers are paid very well for arguing their way around such prior art so that may not kill it off.
There are other groups you can join such as Peer To Patent, which can be used to put forward prior art as well. I would wait until it hits the publication stage (available on PAIR) then submit the prior art to P2P and the USPTO. The latter may cost a little bit of money but you can probably use some of that $250 if you feel strongly enough about it - it would be karmic for the company to fund the fight against their own patent :-)
You'll need to wait for official publication since it's the claims of the submission that you need to discredit. Arguing about how non-novel this is is irrelevant until you see the claims.
Me, I would just cash the cheque and let it go, life's too short for crusades. If you're ever called on to testify in the patent lawsuit, just tell the truth. Getting the patent thrown out after the company has spent $50K+ on the whole process plus court costs will be far more damaging to them than stopping it from filing at all.
Standard disclaimers: I am not a lawyer, I am certainly not your lawyer, this diatribe above is not advice and it's worth every cent you paid me for it, which is a big fat zero :-)