SUB- presubscribe

my client is asking for a way of giving the final customer the option to "program" when the subscription will start.

Since Optimum kind of sell "bundles" of these optimum pills (monthly pack, anual pack, etc). It could happen that a client has bought an anual pack and is happy with the product so wants to pre-suscribe in advance.Maybe it´s not the most usefull feature ever in this case, since people can just wait for the date and subscribe when they feel ready, but my client argues that they dont want to lose this "urgency feeling".