I've never messed around with 38 cases since 357 cases are readily available. For the price of a mold you can buy 500 new 357 cases, so I'm having a hard time understanding why anyone would bother with 38's ?
The "jump" is not the only issue since less of the bullet will be supported by the case. Nonetheless, the "jump" is the only thing you can fix. If memory serves, Skeeter Skelton loaded a dual crimp Ray Thompson design (358156) in 38 cases and was happy with the results.
I would prefer to use a dual crimp, or crimp in a lube groove, rather than having an extra long front band, to reduce bullet distortion when it engraves the rifling.
You could also simply try shooting a standard bullet in 38 cases and see if it shoots OK. The jump may not be all that important providing the bullet is the correct diameter and the gun is cast-friendly.