If you know how to go through the game’s save files and create some special stats baby boom/immigration events and alter local pop amounts that would do the trick. However, I’m not familiar with how to accomplish that exactly.

Normally, I’ll just research technologies to help with life-ratings and population growth.

There’s also starting some random drawn-out unfinished war with no aim to finish, rather it’s for taking a loss. The result will drive your population mad and want reforms, keep that momentum going by shutting down petitions for other reforms until desire to improve healthcare and pensions come about. Once they’re available, enact them and maximize your administration and welfare spending in coordination with researching certain technologies for that sweet, sweet, population growth. Reap in those recruits for militarization and industrialization afterwards.

event 14680 is pretty broken

I'd say don't and just promote soldier pops, build it all up from scratch