Pourdriere: Adding package to jail environment?

[Patrick]

I'm having trouble getting databases/mongodb compiled by Pourdriere
for a 9.2/amd64 environment. I had a similar experience in another
jailed environment (non-Poudriere) which I resolved by first
installing lang/v8 into the environment. I'm wondering if there's a
way in Poudriere for me to install a package into the build jail?
Reading through the documentation, I don't see how to do this.

Patrick