DSL Modems one on Master and one on Slave as individual Backup WAN line

[kostfastnix]

I have a running HA mit two Boxes and WAN with public IPs to generate an appropriate Config, number of VLANs on the LAN side, etc. etc. All works well.
Is it possible to put on each node individually an DSL Modem on a dedicated Interface. As expected, when I started configuring an PPPoE Interface for connecting a Modem on the Master it generates a Gateway which lead to inconsistency with regard syncing the config to the slave.
So I step back from this approach.
The idea is to have one Modem on the Master and on on the slave for Backup purpose. Both connected to DSL lines with different Login Data for PPoE. Is there an feasible solution?
Thank all for suggesting a solution.