The best I've been able to come up with is based on tblAssets.lastseen and uptime. Add a couple of calculated fields to the default query to get you going.
SELECT Top 1000000
tblAssets.AssetID,
tblAssets.AssetName,
tsysAssetTypes.AssetTypename,
tsysAssetTypes.AssetTypeIcon10 As icon,
tblAssets.IPAddress,
tblAssets.Lastseen,
tblAssets.Lasttried,
DateAdd(second, 0 - tblAssets.Uptime, tblAssets.Lastseen) AS LastBoot,
Convert(Decimal(6,2),tblAssets.Uptime / 60 / 60 / 24) AS DaysUp
FROM
tblAssets
INNER JOIN tblAssetCustom ON tblAssets.AssetID = tblAssetCustom.AssetID
INNER JOIN tsysAssetTypes ON tsysAssetTypes.AssetType = tblAssets.Assettype
WHERE
tblAssetCustom.State = 1