As a less expensive alternative to the one mentioned above you can also use white nail polish with a thin coat of gel over the top in the same way as described above.
On clients who have to have a natural looking enhancement (ie - no white tip as a rule) either out of chioce or because of their work, if they are on holiday & fancy a permanent french (one that won't smudge [they can leave the salon once the inhibition layer is removed from the gel] or chip [unless they are digging up spuds with their bare hands!] till their next maintenance} - this is the method I use - refine your acrylic nails on one hand as ususal, paint (I use Orly "White Tips" polish) your french , this polish has time to dry whilst you refine acrylic on the second hand & then again paint on the french. Once you have finished with the second hand the white tips on the first hand should be dry (they need to be or the gel you apply over the top will not set properly) Apply a thin coat of gel over the whole nail not forgetting to cap the free edge & cure (I use IBD clear gel) , repeat on the second hand & voila! - a client who fancies the occasional french can waltz out of the salon as soonas it's cured, no drying time. This takes approx 10 min tops (inc curing time) & seems to be the treatment of choice for the clients who just can't bear [&often do not have the time] to wait for their polish to dry!