A pretext for...is never wanting
何患无辞
on the pretext of illness
假托有病
on the pretext of imperial edict
矫诏
excuse sb. from
免除某人(做某事)
make use of anything as a pretext for blackmailing
借端讹诈
excuse sb. from a task
免除一项任务
To make a pretext to blackmail
借端敲诈
excuse from examination
免试录用
To make use of anything as a pretext
借故生端
excuse me,but I must be leaving now
失陪
make use of anything as a pretext for provocation
借故生端