HTTP GET request over PPP using UART to Linux Device

Question

I am attempting to establish a PPP connection between an nRF9160 and a Linux device over a UART (hardware flow control is optional). The goal is to allow these devices to share their internet connections, and also communicate directly with each other via HTTP. 
 
 I am unclear how to setup a UART as the PPP interface when the UART is not connected to a gsm modem. 
 
 I see examples that involve establishing a PPP connection over the cellular modem: 
 https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/net/gsm_modem 
 https://github.com/nrfconnect/sdk-nrf/tree/main/samples/nrf9160/modem_shell 
 https://github.com/nrfconnect/sdk-nrf/tree/main/samples/nrf9160/https_client 
 https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/net/sockets/http_get 
 
 I also see examples where it appears a PPP connection is established with the Linux host; however, the app runs in QEMU, and does not involve a UART. 
 https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/net/sockets/echo_client 
 https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/net/sockets/echo_server 
 I have made some attempts at setting this up, starting with establishing a PPP connection. As I dug through the source ( https://github.com/nrfconnect/sdk-zephyr/blob/main/drivers/net/ppp.c ), it seems very focused on UARTs connected to gsm modules. I'm wondering if what I'm trying is no possible with the SDK "out of the box" as I originally thought. 
 Is it even possible to use PPP to send HTTP through a UART that connects to a device running Linux? From a high level, what would that involve? 
 Any high-level suggestions or guidance would be greatly appreciated. Thanks!