How to raise PPTP client connect in parallel with Softether VPN Server and teach it to let clients into the pptp subnet?

Question

linux

Essence:
There is a server based on Debian 7, on which the multiprotocol Softether VPN Server is installed and operates (set according to the guides). It is configured and accepts connections via L2TP / IPsec, OpenVPN and through its utility for vend.
It is also a "Virtual HUB", due to which a small convenient LAN is organized from remote PCs and mobile devices.
Addresses that are received by server clients, like 192.168.*.* and go to the Internet through it.
Recently, the IP-telephony service has appeared as a complex service that works EXCLUSIVELY through VPN (login / pass access is provided and is part of the complex service). Those. A PPTP connection is created on the mobile device, and thus the device gains access to the internal network of the form "10.250.*.*" where the IP-PBX is located. In the Sip client, credentials + the internal address of the sip server are entered and calls are made.
As a result, we have a mobile device with TWO VPN connections that need to be reconnected in order to gain access to a particular network (192.168 and 10.250, respectively) which is extremely inconvenient for a certain category of users, especially for those who do not want and cannot go into technical details, the basics of information security, and does not want to bear the cost of convenience.
Question: Is it possible to raise a PPTP client connection on the same Debian server where Softether VPN Server is running and somehow allow it to let clients also into the 10.250.*.* subnet?
Thank you.