Create a user variable that is set from the command line.
If you're running the ssis package from a SQL agent, you have to modify the command line to include the value to set to the package variable.
If you're running the ssis package from the DOS command line, you have to use the appropriate command line values.
If you're running the package from visual studio, just set the variable manually, and execute the package.
To pass the variable to the url, you have to use an expression that will append the variable's value to the URL.
When I get to work, I'll modify this response to include an example of the appropriate command line parameter.
In the mean time, google is your friend if you want to finger all of this out on your own. That's how I did it.
PROMISED UPDATE
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The following command line is valid for both running the package using DTEXEC on the DOS command line, or running the package from a SQL agent:
/FILE "\\fullpath\ssispackage.dtsx" /X86 /CHECKPOINTING OFF /REPORTING E /SET "\Package.Variables[User::pkgMyVariable].Value";0117
The /SET parameter is what you'll be specifying for your file name.
If you're not running this package from an agent or with DTEXEC, this information does not apply to you.