I think you are trying to solve a non existent problem. If you want streamlined, then use a long hose primary 2nd stage and a short hose alternate, attached to a bungee necklace. You can then choose a nice short corrugated BC inflator hose with a properly sized short LPI hose.
There are all sorts of issues with the inflator/alternate 2nd stage combos that have been debated on this forum for years. They are polarizing; some divers like them, others don’t. If you wanted to, you could read all those discussions, but you might not have enough time left over to actually dive again!
But, if you insist on the octo/inflator, you’ll want a longer than necessary corrugated hose, which adds bulk in your chest area. This might already exist on your current BC, you can measure it. You’ll want at least 18”. You’ll also want a longer primary 2nd stage hose, which is fine if it’s routed correctly. There are lots of threads about that issue too.
You might want to have a look at what technical divers who routinely dive in tight spots use for a set up. Streamlining isn’t a convenience in those environments, it’s a critical safety issue. Of course not everything that tech divers do is applicable to recreational diving, but some things are.