Courts complicit in framing future DUI murder charges?

There is an interesting post on Lawrence Taylor's DUI Blog about linking previous DUI convictions to a future murder charge.  According to Mr. Taylor, upon conviction for DUI in California, the judges make defendants sign a statement saying that they understand that DUI is dangerous. That statement is then used to predicate murder charges (rather than manslaughter) if the person later kills somebody while driving drunk.

Prosecutors have been trying to make DUI murder for years. But this new strategy is the first that I've heard of the courts becoming involved. It seems to me that there would be a coercion argument. In other words, yes the person signed the statement, but did they understand it, and did they sign it willingly? Later, in a murder prosecution, the state would still have to prove the mens rea (mental element), which I believe would be difficult or impossible based only on the previously signed in-court statement. The prosecution would likely have to prove that the defendant not only understood it at the time it was signed, but also at the time of the accident that forms the basis for the murder charge.