This is correct for a standard DHCP pool and it looks like it is possible to add any DHCP option. However VIA seems to only use the IPSEC address pool found under
Advanced Services > VPN Services > IPSEC - Address Pools.
There are no options in the GUI but I was hoping there may be some command line options. The command 'ip local pool ....' does not seem to have the same options as ip dhcp pool.