You have to look for the "sweet spot" on the quill
The point where the stem just does not want to bend well and then plan on using only the flexible part. That might mean tying in somewhere up the hook shank rather than at the normal logical tie in point.
Then there's superglue... the duct tape of fly tying
When you're getting close to what should be the tie off point, dose the hackle stem with superglue and hold it in place. When it's secure, clip the "pokey thingy" and then tie it down... or not.
If the hackle is glued in well, you won't even have to tie it.