It's not an easy question to reply. You are looking for a solution to get her a female ejaculation and keeping her hymen intact. Is it? Thats not a child's game.
What does it mean by virgin to you, a girl having her hymen intact, is that a virgin? A virgin is a person who has never had sex before. Do you mean a girl giving blow job, having analsex and this finger fucking is a virgin just because her hymen is intact? We need to think more on the definition then.
Female ejaculation can be achieved with G Spot stimulation, I guess this has been spoken before. by tickling on G Spot with finger, on a finger inside her vagina on frontal vaginal wall helps to accumulate ejaculation fluid generated from various glands on urethral gland. both urethral gland and bladder has same outlet of U stop where the urine comes out. Thats how it works.
Now you can locate G-spot with your experience or knowledge. Some says its on 1.5 inch, somesays its on 3 inch, I will say, its exactly below the pelvic bone, if the bone is higher up, its deeper, if its lower down, its closer to vaginal entry. Now, where the hymen is? its no seal that blocks the passage, rather more of a thin membrene at the entrance. How long are you sure you can keep the thin membrene intact and do a finger fuck with rubbing G-spot?
Nothing much wrong with your question, maybe your intention is different, but it is not as simple as I am writing here. When a female ejaculation happens, it usually follows a deep orgasm. The body movement will be tends to impossible to save the hymen and do all the tricks. It doesnot happen in that way, two fingers inserted upto two to three knuckles, not an easy job to save that flimsy poor hymen.
When insert fingers and rub the G-spot, the way is keep moving the fingers on alternate motion of moving like "come here move. When the pressure comes, fingers need to make flat and give upward press on the urethral gland. Most women are capable of female ejaculation, but most men doesnot know how to do it right.