I used a long time ago PCI-E splitter on 775 socket motherboard based on Intel P43 chipset which older than Intel H81.
AMD GPUs worked well, but Nvidia GPUs don't detected correctly on it.
Most mining board used the same chip which used on PCI-E spliters e.g. Asrock H110 Pro BTC+, ASUS B250 Mining Expert (ASMedia ASM1187, splitters usually used for 4-port ASM1184)
Success depends on many reasons, but mainly the implementation of PCI-E bus lines on the motherboard, presence 4G Decoding in the BIOS for proper allocation of address space, the freshness of the chipset for example on H110 newer the chance is much higher, on older chipsets only experimentally with a particular model.