Hello W.,
From your diagram:
If you never use link with "API 1" or "API 2" outside Integrations, a workaround is to use long description ('[' and ']'), sub-diagram ('{{' and '}}'), and an hidden arrow as:
Rectangle INT #white [
<b>Integrations
{{
usecase "API 1" as A1
usecase "API 2" as A2
A1 -[hidden]-> A2
}}
]
Then, we observe the expected result:
That's only a workaround...
If that can help,
Regards,
Th.