Installation should have been windows 7 and then windows 8, windows 8 would have created a duel boot menu if both drives were connected.
I don't know what you mean by "I am very near my 3 installs limit" you can reinstall windows as many times as you like on the same computer.
You could try Visual BCD Editor CLICK HERE this repairs the boot menu. As it's the first time I've seen this I tried it on a spare computer, I connected another drive with a second OS and it seems to work. Clicking on auto repair should create a duel boot menu.