That is absolutely possible. While it is always better to keep shares in your demat account, there is the possibility of leaving these shares with your broker in the pool account. Since the broker is not permitted to keep shares in the pool account and has to necessarily transfer it into your demat account by T+2 days, the onus is on you to give a “Running Authorization Letter”, which can enable your broker to keep these shares in the Broker Pool account. These shares can be used by you as margin for taking trading positions in the market without worrying about putting n additional cash. In fact, you can give a running account authorization to the purpose using the form as under.
Please note that this agreement is not mandatory and you must sign this agreement only if you are absolutely comfortable doing this. Otherwise, leave the shares in your demat account. You need to read the fine print of this agreement as it includes clauses like your broke can sell shares if the price falls and that the broker can also transfer the shares into another demat account. This is a useful and simple way of leaving shares for margin instead of again trough the demat route. But you must use this facility sparingly.