connect a second adsl modem/router as a slave to 1 ISP account

I've been searching everywhere for info on this, and people here seem
to be the most knowlegable...so here goes:-

I have 2 ZoomX5 ADSL modem/routers. 1 is connected in one corner of my
house. I'd like to connect the other at the opposite end, upstairs. I
know I could use Cat5 and run it from the first to the second PC no
problem, but a better solution for me is to just connect a 'slave'
modem upstairs, where I already have a phone line ready to go.

I can't connect the second modem as pre-configured - it 'knows' I'm
already logged into my ISP. Is there any way to configure the 2nd
ZoomADSL to be a slave without being physically connected to the first?
I read somewhere that I could have multiple PPPoE's? I'm not very
technical with networks, but logically I think I'd be able to have a
slave...

Wireless is not an option - I've tried but we're talking multiple walls
of concrete, plus a floor, it makes it about 40ft - I need about 100ft
line of sight (or 150-200 if I were to run Cat5).

Thanks for any help in advance.

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