unfortunately there isn't much you can do about it because you are limited by the trading rules of the platform (
https://support.binance.com/hc/en-us/articles/115000594711-Trading-Rule) which is 0.001
BTC worth of altcoins or nearly $8 with current rate and if you have less than that value then maybe it is not worth selling it!
the only workaround that i can think of is to transfer those coins to another exchange which allows lower order sizes. i believe cryptopia still allows such small orders and has most coins. but make sure that the withdrawal fees of those altcoins are not higher than your balance and also make sure the wallets on both exchanges are operational.
It won't be worth doing that the fees of both the exchanges will suck up most of his altcoins and having the coins on binance is probably the worst situation there fees is so high for most of the altcoins
What he can do instead is buy those coins from exchanges like shapeshift and directly transfer it to binance (keep in mind the minimum trade rule) and then you can sell it off
if he wants to buy more coins to cover the difference then i don't see any reason for using another place to buy them such as shapeshift. he can simply place a buy order at a lower price to buy the difference inside Binance itself and them place a sell order at a little higher price to sell all that he got. this is better because you can buy near support for instance and you set the price but buying from ShapeShift you will have to pay a higher price that they give you.
this is a little risky though because of the price fluctuations and the fact that some coins don't have the volume needed for you to fill an order fast!
