How to Create VPN in 2 Difference Network without Permanent Tunnel

My Situation

I have 2 networks named N1 and N2(totally isolated). N1 have VPN connection. I want to setup VPN access at N2 but the connectivity is not directly from ISP. The connection need from N1. And i did not want establish permanent connectivity/tunnel from VPN N1 and VPN N2 to maintain network splitting.

P/S: I use 2 difference VPN hardware

Thank you