Maven to include JAR that is generated by that build - maven

Question

Normally we use dependency tag in pom.xml to have Maven include a JAR on the classpath and it also packages that dependency.
What if the JAR is generated in a step of the same project's build? I mean, it's not the compile plugin that generates it, it is a JAR without any java source and an external executable creates it.
I can use maven exec plugin to have my JAR generated and maven install plugin to have it installed to my local repository. But still I can't have it as a dependency in the same project: No matter which phase I put my JAR generator command in, the dependency check will happen before that and fail because the JAR does not yet exist.
Is system scope dependency my best choice? Then I need to give up packaging. And it's deprecated. And the JAR needs to be outside the project directory.
Or the JAR generator must be in a separate pom? Also not very nice because the JAR is only used by this one project.
Can I configure the dependency plugin to defer the dependency check and download to compile phase?
Any other solution?
This pom almost works, but first time I need to install the generated thing manually to the repo.
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<artifactId>something-parent</artifactId>
<groupId>something</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>something-sample</artifactId>
<properties>
<jnbridge.path>C:/Program Files (x86)/JNBridge/JNBridgePro v9.0</jnbridge.path>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<executions>
<execution>
<id>generate-proxies-jar</id>
<phase>generate-test-resources</phase>
<goals>
<goal>exec</goal>
</goals>
</execution>
</executions>
<configuration>
<executable>jnbproxy.bat</executable>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>8</source>
<target>8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-install-plugin</artifactId>
<version>2.4</version>
<executions>
<execution>
<phase>process-test-resources</phase>
<goals>
<goal>install-file</goal>
</goals>
<configuration>
<groupId>jnbridge.local</groupId>
<artifactId>proxies</artifactId>
<version>0.0.0</version>
<packaging>jar</packaging>
<file>${basedir}/proxies.jar</file>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
<dependencies>
<!--
Yes, these are true system-scope dependencies. JNBridge is expected to be
installed on the system wherever this project is built.
-->
<dependency>
<groupId>com.jnbridge.org.apache</groupId>
<artifactId>bcel</artifactId>
<version>5.1</version>
<scope>system</scope>
<systemPath>${jnbridge.path}/jnbcore/bcel-5.1-jnbridge.jar</systemPath>
</dependency>
<dependency>
<groupId>com.jnbridge</groupId>
<artifactId>jnbcore</artifactId>
<version>1.0</version>
<scope>system</scope>
<systemPath>${jnbridge.path}/jnbcore/jnbcore.jar</systemPath>
</dependency>
<!--
This one will be installed to local maven repo in the process-test-resources phase,
as defined in the project/build/plugins section of this file.
-->
<dependency>
<groupId>jnbridge.local</groupId>
<artifactId>proxies</artifactId>
<version>0.0.0</version>
</dependency>
<!-- other dependencies... -->
</dependencies>
</project>