Aaron sent in a question about a usage that he first noticed at the age of nine, learning Allan Sherman's "hello mudda hello fadda" for an elementary school assembly:
Now I don't want / this should scare ya,
But my bunk mate / has malaria.
He has also seen a similar use of irrealis should from time to time in old jokes:
Q: Mom! You haven't eaten in three weeks? Why not?
A: I didn't want my mouth to be full you should call.
Aaron observes that he hears things like this particularly among older Americans of Jewish descent", and wonders whether it's an English imitation of a Yiddish construction. There's a useful discussion in the xkcd echochamber ("You want I should" 10/28/2010), which seems mostly to agree that this is a Yiddishism, and points to usage by Zoidberg and other Decapodians in Futurama, e.g. here:
Sure, you can vote for Shkinadel — if you want there should be a recession!
This somewhat counters the Yiddish association, since the Blues Brothers' fictional background involves "growing up in a Roman Catholic orphanage in Rock Island, Illinois and learning the blues from a janitor named Curtis". On the other hand, Aykroyd is Canadian, and there may be a more general confusion in Hollywood between Yiddishisms and non-standard English.
Update: An apparently satirical document, the Obleweiss Will, has several similar examples in the context of English influenced by the German varieties spoken by immigrants to Texas:
I, Herman Obleweiss, am writing my will mineself. That dam lawyer want he should have too much money [...] First thing, I want, I don't want my brother-in-law Oscar get a dam thing I got. He is mumser. [...]
I want that Hilda, my sistem, she gets de north sixtie akers where I am homint now. I bet she don't get that loafer husband of hers to broke twenty akers next plowing time. She can't have it if she let Oscar live on it. I want I should have it back if he does. [...]
Momma the rest should get but I want it that Adolph should tell her what not should do so no more slick Irish vokum Cleaners Salesmen. [...]
I want that my brother, Adolph, should be my execter and I want it that de judge should make Adolph plenty bond put up and watch him like hell. Adolph is good business man but only dumkopt would trust him.
Update #2 — Here's another suggestion that the "want PRO should" construction existed in informal varieties of American English before there was much influence of Eastern European immigrants. From An Uncommon Soldier: The Civil War Letters of Sarah Rosetta Wakeman, Alias Private Lyons Wakeman, 153rd Regiment, New York State Volunteers, a letter dated 11/24/1862:
My Dear Father and mother and sister and brothers, one in all,
I receive you letter on Sunday the 23. I was very glad to hear from you and learn that you were all well. [...] I was only 7 miles from Binghamton up the river. I didn't go to the fair. When i got done work I went on the canal to work. I agreed to run 4 trips to Utica for 20$ in money, but this load of coal was going to Canajoharie, Montgomery Co.
When I got there i saw some soldiers. They wanted I should enlist and so i did. I got 100 and 52$ in money. I enlisted for 3 years or soon as discharged. All the money i send you i want you should spend it for the family in clothing or something to eat. [...]
Mother, i will tell you where my little Chest is. It is upstairs over the bedroom in the garret. Let Robert go and climb up by the stove pipe hole and he will find it on the left hand side toward the road up in the corner. I want you should keep all my things for me for i believe that God will spare my life and that I shall see you all again face to face before i die. Father, if you will send me some postage stamps I will be very thankful for them. I want to drop all old affray and I want you to do the same and when i come home we will be good friends as ever.
_____Good-by for the present.
_____________________________________Sarah Rosetta Wakeman