You're right not to do the multiply the hours trick as sooner or later someone with knowledge will pick up on it and your name will be mud.
If it's a normal referral like:
Client: Who can I get to do this?
Development company: We've used this guy in the past and he's very good, here's the card for JS.
Then open discussions with your normal rate.
.....
If it's more a case of:
Client: Who can I talk to about this?
Development company: We'll have JS call you.
Then you got troubles as this implies you're working for of through the development company.
..........
Essentially, if the client knows up front you're freelance and the development company rates don't apply to you, you're OK. If the company implies you work through them there could be issues.
.........
Does the development company hand out your card or your web site URL or just the phone number as ways of contacting you?
If it's your business card, try printing your rates on the back of the card with a note on the front - rates on reverse - most people will know then what the real situation is.
Have your rates on your web site and try to encourage referrals through that, so they'll see the rates up front too.
Otherwise, just make it clear on your answering machine and how you answer the phone that you're an independent contractor and have your own rates.
..........
What you say implies you bill the client direct and not through the development company. That makes your contract with them yours and nothing to do with the development company. If the client insists on the development company rate you can take the risk of loosing them by pointing out they're employing you and NOT the development company as the company only referred you on. Or you can bite the bullet and charge the lower rate, but that has the problem of explaining the higher rate later.
As a general legal point of view, you need to inform the client of YOUR rates in the first discussions. This is your work not the company's work. I'd suggest offering a mild 'new client' discount as a get them in the door thing and make it clear it's a discount only on the first job.