I'm guessing you mean the hold switch, not the pause button...
Anyway, the answer is "not really". It's possible to build a bootloader which doesn't check the hold switch and always starts Rockbox, or even to not use the bootloader at all and just install Rockbox directly to the firmware partition, but then Rockbox will reset its settings to defaults every time you boot it up with the hold switch turned on, since that's what the switch does if it's turned on *after* the bootloader but before Rockbox has booted, so you would need to build a custom build of Rockbox itself as well which doesn't have that functionality either (and then you'll have to do a custom build forever to get any updates).
I've considered how to solve this but haven't come to a reasonable conclusion yet; probably the best thing to do is stop using the hold switch as the mechanism for *either* of these features on ipod, but this is a UI change (and some ipods apparently had a problem using a button for dual-boot) so it's not something I'm just going to change without more consideration.