[Feature request] Choose padding byte while using rgblink's overlay feature

[marcrobledo]

According to documentation:

-p pad_value, --pad pad_value: When inserting padding between sections, pad with this value. Has no effect if -O is specified. The default is 0.

It is not possible to set the padding value if usign the --O/-overlay feature.

It makes sense since the overlay file is already assembled and has data on it. However, I miss this feature when expanding the ROM.
I'm working on a ROM hack that needs to switch to a new bank, read a byte (which will be the OAM attribute) in the current [hl] then return to the original bank. It would be great if I could choose the initial value to be $00 of those new banks instead of doing my own workarounds.