Using checkbox as radio button in CF7

I am looking for a way for users to select one of the few options in Contact Form 7 for a list of weeks. They should basically behave like radio buttons (only one selectable at a time, plus unselect any previous selections).

The problem is that I can't use plain radio buttons in first place, because the name attribute for each radio button would be different.

Thanx)

<span class="wpcf7-form-control-wrap checkbox_custom-3">
<span class="wpcf7-form-control wpcf7-checkbox_custom chkclass srok_razmesheniya" id="ch1">
<span class="wpcf7-list-item first last">
<label>
<input type="checkbox" name="checkbox_custom-3[]" value="20">
<span class="wpcf7-list-item-label">
1 week</span>
</label>
</span>
</span>
</span>
<span class="wpcf7-form-control-wrap checkbox_custom-4">
<span class="wpcf7-form-control wpcf7-checkbox_custom srok_razmesheniya" id="ch2">
<span class="wpcf7-list-item first last">
<label>
<input type="checkbox" name="checkbox_custom-4[]" value="40">
<span class="wpcf7-list-item-label">
2 weeks</span>
</label>
</span>
</span>
</span>
<span class="wpcf7-form-control-wrap checkbox_custom-5">
<span class="wpcf7-form-control wpcf7-checkbox_custom srok_razmesheniya" id="ch3">
<span class="wpcf7-list-item first last">
<label>
<input type="checkbox" name="checkbox_custom-5[]" value="60">
<span class="wpcf7-list-item-label">
3 weeks</span>
</label>
</span>
</span>
</span>
<span class="wpcf7-form-control-wrap checkbox_custom-6">
<span class="wpcf7-form-control wpcf7-checkbox_custom srok_razmesheniya" id="ch4">
<span class="wpcf7-list-item first last">
<label>
<input type="checkbox" name="checkbox_custom-6[]" value="80">
<span class="wpcf7-list-item-label">
4 weeks</span>
</label>
</span>
</span>
</span>