Inbound traffic with dual wan

Hi,

currently i'm using a leased line with a /24 public ip-subnet. these ips are configured as additional addresses on the external interface and then dnatted to internal servers. Sounds common for me.
in the near future i'm switching to a multihomed stub, connecting with two providers via bgp. Besides bgp-configuration (which will be hard enough for me anyway!) there is one thing i cannot imagne how to realize it.
i cannot set public ip-addresses as aditional interfaces on both wan-interfaces.
How can inbound traffic e.g. to internal webserver be accomplished with two wan-interfaces and bgp?

thanks in advance
Toni

ASG220 v9.103.5