This isn't the way things by default work. You can try submitting a support ticket, but as it doesn't strike me that there's any real good reason for needing this, I suspect it would be one of those things where they say unless you have a good reason for it, they'd prefer that you just left things the way they've designed it to work.
I'm open to being corrected on this, but there's a decent argument for making sure that the one domain you have assigned a unique IP in fact has a unique IP rather than having one that's shared among a couple of sites that you own.
That said, I know that because of the way PS works, all sites on a Dreamhost PS server get the same IP address and that address is guaranteed to be your own.
The way SSL works, unless you purchase an expensive wildcard certificate, you need to assign a unique IP address to each domain that you have a certificate for.
What are [color=#CC0000]50DISK50[/color], [color=#CC0000]3DOM50[/color], and [color=#CC0000]1IP1DOM50[/color]?
They're Dreamhost coupons!