If you are the originator of the work, then you can license it to as many people as you want, under as many different license agreements as you want. The GPL imposes conditions on the licensee, not on the copyright owner!1 The fact that you give me access to your code under the GPL license for one price has no bearing whatsoever on the license conditions (and price) you give to someone else.
The clause of the GPL that you're asking about binds other people who receive your work under the GPL. It does not bind you, so it is totally irrelevant to any other license agreements you might make.2
However, people are usually interested in loopholes to the GPL because they want to make use of GPLed code owned by other people, without having to release the source of their own modifications. In this scenario, you cannot do what you propose, because you have no authority to distribute only the binaries under the commercial license (regardless of price). You can decide not to distribute at all, or you can distribute under the GPL for any price you like (necessarily including source code in the same price). Those are your options.
Dual-licensing isn't really a "loophole". It doesn't somehow "get around" any obligations of any license agreements, it just makes use of the fact that you are not a licensee of your own work; there are no license terms governing your use of it. If you do actually have obligations under the GPL (because you're a licensee of someone else's GPLed work), then you can't dual-license.
1 It is possible for two parties to make a contract where one party will exclusively license their work to the other. That contract would restrict them from also giving the work to other people under other licenses, but there is no such contract involved in typical uses of the GPL. Certainly it's not in the GPL itself, which is merely a one-way grant of permissions to distribute the work under certain conditions, not a two-way exchange of obligations.
2 Technically you can even give binaries of your own original code (not a derivative work of anything else) without the source code, licensed under the GPL. The fact that you gave them permission to distribute the binaries as long as they also distributed the source does not obligate you to give them the source. You're the owner! You don't need anyone's permission to distribute your own work.
However it's a pointless thing to do, because the effect is just that they can't distribute the binaries (since they don't have the source, and you only gave them permission to distribute the binaries if they also distribute the source). You might as well just use a license that says "Do not distribute".