It IS possible to root longer stems to try as tree rose stocks, but it either takes mist to prevent them from drying out, or wrapping them similarly to what I demonstrated on my blog (linked below). Before striking them as cuttings, you want to thoroughly remove the growth buds from the whole length, EXCEPT for the top two or three of each stem. If they aren't removed, you will have suckers from their growth. That's what causes the majority of suckering issues in tree roses.

If you are rooting under mist, you CAN chip bud and root them simultaneously, but without mist, your budding chances are slim. For budding of any type to succeed, the sap has to be freely flowing from root to tips so the scion (bud) doesn't dry out and fail. Since the cuttings won't have roots to absorb water and they won't have a lot of leaf surface to both feed the cutting as well as assist in the transpiration (sweating and drawing) of water through them, there is bound to be water stress to the bud, probably causing it to fail. Rooting under mist keeps the entire cutting (and bud) properly hydrated so neither fails due to being too dry. If you don't have mist available, you will need to root the stocks first, then when they are actively growing next spring/summer, attempt your chip budding then.

You may try wrapping them in damp newspaper and plastic to pre callus them prior to potting, as I showed in the link below, if the season is right (as explained in earlier posts on the blog), or you may strike them as you would your traditional cuttings but use the white plastic trash bag pieces as I show later in the linked post below. Both can work, permitting you to root longer pieces for stock use. But you should reserve your chip budding until they are actively pushing new foliage from the top buds as that indicates there is good sap flow to support the buds until they knit to the stock. Good luck! Kim

Here is a link that might be useful: Longer wrapped cuttings for standard stocks