Нельзя, у них разные точки входа. Можете попробовать через rewrite на уровне веб-сервера. Проще всего админку в такой структуре вешать на адрес admin.site.com.
ServerName www.yii2-start.domain # You need to change it to your own domain
ServerAlias yii2-start.domain # You need to change it to your own domain
DocumentRoot /my/path/to/yii2-start # You need to change it to your own path
# You need to change it to your own path
AllowOverride All
<VirtualHost *:80>
ServerName www.yii2-start.domain # You need to change it to your own domain
ServerAlias yii2-start.domain # You need to change it to your own domain
DocumentRoot /my/path/to/yii2-start # You need to change it to your own path
<Directory /my/path/to/yii2-start> # You need to change it to your own path
AllowOverride All
</Directory>
</VirtualHost>
Попробуйте написать автору сборки прям на гитхабе. А если все же не принципиально, то вешайте на поддомен. В apache для этого нужно создать два виртуальных хоста на backend и frontend отдельно.
Как-то так, наверное. Точно не скажу, не работаю с апачем.
<VirtualHost *:80>
ServerName www.site.domain # You need to change it to your own domain
ServerAlias site.domain # You need to change it to your own domain
DocumentRoot /my/path/to/yii2-start/frontend/web # You need to change it to your own path
<Directory /my/path/to/yii2-start/frontend/web> # You need to change it to your own path
AllowOverride All
</Directory>
</VirtualHost>
<VirtualHost *:80>
ServerName admin.site.domain # You need to change it to your own domain
ServerAlias admin.site.domain # You need to change it to your own domain
DocumentRoot /my/path/to/yii2-start/backend/web # You need to change it to your own path
<Directory /my/path/to/yii2-start/backend/web> # You need to change it to your own path
AllowOverride All
</Directory>
</VirtualHost>