Another thing you can try is offering your customers 2 quotes. One for a faster, in-house printing with vinyl on coro, and one for the slower, outsourced direct print.
At my last job, we did tons of coro signs with vinyl. Our customers wanted 2-10 signs "right now". We couldn't farm those out in a reasonable timeframe for our customers, and we didn't see it as economical to lose profit on outsourcing the one-offs. But when they would ask for larger orders, we'd offer them the choice. Did they want to pay a premium for faster turn around, or wait for the outsourcing with a lower price point. A lot of times, they'd still rather pay the higher price for the faster service, because they wouldn't plan in advance of their needs. It would make a busy 1-2 days, but it kept us open and profitable.
In instances like this, I prefer to let the customer make the call. I can make money either way. One gives me a ton of work, one gives me more time. Both make profit. Depending on the other jobs we have going, I might try to persuade them one way or the other - like if we're dead and I've got guys not doing anything, I'd lean towards in-house. But it varies from day to day.