Two SPI NOR Flash chips in parallel, possible?

is it possible to hardware mod a router to have two spi flash chips , with different chip selects and mount them as one chip ? lets say two 4MB chips, and openwrt sees them as 8 MB ? or maybe sees the second chip as an mtd partition?
note: I'm fully capable of any hard / soft mod required.

Not really, SPI means serial peripheral interface.

The select and clock are parallel but the io is serial


Sounds like you are looking for "mtd-concat". This feature is available for openwrt 4.14 and 4.19 and currently, some ath79 buffalo devices are already using it.

If you hard to find one more CS pin you can use the same CS0 pin as C̅S̅1 (negative or reverse) by using single inverter gate.
(But use NOR SPI Fash instead SD-Card)