First thing which you probably already know - diazepam is not lethal alone, even if you take 1000 pills. The alcohol combination can make it deadly, but you would need a large dose of alcohol, verging on alcohol poisoning, which would need to be carefully chosen and managed. The sequence absolutely must be to first get drunk and then take diazepam, not the other way round, because you'll fall asleep long before drinking enough to be lethal. If you took them at the same time, the diazepam would likely kick in before you have a chance to drink enough, so that wouldn't work either. You would want to reach a level of drunkenness which is not causing nausea, which is difficult, but otherwise the pills will just be vomited out. I wouldn't personally count on antiemetics to be able to manage alcohol nausea, unless you "practise" a few weeks before to find out where your limit is for nausea. Short version is get as drunk as you can (not all in one gulp, but more gradual) without feeling sick then take pills. If you're feeling adventurous, one way of avoiding the vomiting problem would be to rectally administer diazepam. This does work, but you'd probably need to do some work on crushing the pills and using water to extract the active ingredient. Then, if you vomit, you do not lose the dose. Whichever way, adding in a bag would make it more likely to be effective. One last comment - if you have access to better options then use them, as this is something with a high rate of failure.