Thanks all.

I'll head to store for the agave nectar, that seems to be something fairly common in the canned juice section.

This is what I will try first using it:

1 OZ Whey protein concentrate (80% protein) 23g protein, 100 cal
1 OZ Maltodextrin (100%) 28g carbo, 112 cal
3 OZ Agave nectar (6tbs) 90g sugar, 360 cal.
Total calories about 570

This might be a bit dense so may need to cut with milk or water. Milk of course adds calories and protein and carbs, all good things so likely a better choice.