yiaana on "proven donor sperm"

Hi all -
Would love to get others' opinion on this?
I have been trying to get pregnant for a long time.
Last cycle we used DP's eggs for the first time. We used donor sperm and got a great fert rate.
I just checked and the donor we used is listed as only having a limited supply that is reserved for sibling conception only. When I told DP, she hit the roof. I hadn't really thought about it, but what she said makes sense. Why should someone who had success get the sample over us? Why is it more important that their child be able to have a genetically related sibling (through the anonymous donor) than that we be able to get a child?
At first, I said to DP, well, there are other samples. And she pointed out that how will I feel if we don't get a good fert rate.
She suggested we lie and say we do have a child from this donor. I'm guessing that they will ask for proof, but who knows?
DP's other idea is to request that they allow us to buy one vial because this is our last try, our age, etc. etc.
What do people think?