Ubuntu 19.04 live USB fails to boot on optimus system with CPU soft lockups

[Rocko]

The default configuration of the 19.04 live USB (as of 2018-01-14) fails to boot on my optimus system - it locks up with CPU soft lockups on multiple CPUs unless I manually edit the grub boot to add modprobe.blacklist=nouveau.

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: ubiquity 19.04.4
ProcVersionSignature: Ubuntu 4.18.0-11.12-generic 4.18.12
Uname: Linux 4.18.0-11-generic x86_64
ApportVersion: 2.20.10-0ubuntu18
Architecture: amd64
CasperVersion: 1.401
CurrentDesktop: ubuntu:GNOME
Date: Tue Jan 15 14:02:35 2019
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz modprobe.blacklist=nouveau file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu 19.04 "Disco Dingo" - Alpha amd64 (20190112)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=C.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)